Exhibit 99.1

3050 Spruce Street, St. Louis, MO 63103 USA

Tel: (800) 521-8956 (314) 771-5765 Fax: (800) 325-5052 (314) 771-5757

For questions, contact:

Kirk Richter

Vice President and Treasurer

(314) 286-8004

FOR IMMEDIATE RELEASE - St. Louis, MO, April 24, 2012

SIGMA-ALDRICH (NASDAQ: SIAL) REPORTS Q1 2012 DILUTED EPS OF $0.96, WITH DILUTED ADJUSTED EPS OF $0.99. SALES INCREASE 5% FOR Q1 2012. FULL YEAR 2012 DILUTED ADJUSTED EPS OUTLOOK OF $3.90 TO $4.05 REAFFIRMED.

HIGHLIGHTS:

2012 Results (all percentages are to comparable periods in 2011)

2012 Outlook (all percentages are compared to full year 2011 results)

CEO’s STATEMENT:

Commenting on first quarter 2012 performance, President and CEO Rakesh Sachdev said, “We are pleased with our reported sales of $665 million and diluted adjusted EPS of $0.99 which are the best quarterly results in our history. The 4% organic growth in our Research business was slightly higher than our expectation, even as uncertainties in the global economic environment and in pharma and academic research funding in the U.S. and Europe continued. SAFC had its strongest quarter ever with sales of $197 million. As expected, the organic sales growth rate for SAFC in the first quarter was in the low single digits due to the pre-buy in the SAFC Bioscience business in early 2011, temporary market weakness in the LED markets and production capacity constraints in Hitech. We continue to expect sales growth in SAFC to move from low to mid single digits in the first half of the year to low double digits for the second half.

Following the acquisition of BioReliance in January 2012, we continued to pursue our M&A strategy to add bolt-on businesses with the recently announced acquisition of Research Organics, a leading supplier of high purity biochemicals for use in life sciences markets. This acquisition is an outstanding complement to SAFC’s existing raw materials portfolio and is expected to help us provide our customers more innovative and enhanced quality solutions and true dual sourcing of biological buffers.”

Sachdev concluded, “We’ve reaffirmed our organic sales expectation for 2012 of mid-single digit percentage growth. Our plans are to continue to execute on our Research business’ strategic initiatives to drive sales of our analytical chemistry, biology and materials science products, and to deliver high single digit organic sales growth in SAFC. We also plan to continue to enhance our e-commerce and Asia Pacific and Latin American market sales. In addition, the acquisitions of BioReliance and Research Organics are expected to add roughly 6% to Sigma-Aldrich’s sales growth in 2012. We’ve also reaffirmed our diluted adjusted EPS outlook for 2012 in the range of $3.90 to $4.05. Our plan is to continue prudent cost control without sacrificing a commitment to longer term growth initiatives as we deal with market uncertainties. Our management team remains fully engaged and committed to deliver this performance.”

2012 RESULTS:

Reported sales for the first quarter of 2012 of $665 million increased 5% over the first quarter of 2011. Excluding changes in foreign currency exchange rates which reduced otherwise reportable sales by 2% and acquisitions which increased sales by 4%, first quarter organic sales growth was 3%. First quarter sales for the Company’s Research business grew organically by 4%, driven by strong growth in the Asia Pacific and Latin American regions. First quarter sales for the SAFC business grew organically by 1%

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over the first quarter of 2011, in-line with expectations. SAFC sales were impacted by tougher comparisons related to the customer pre-buy in the SAFC Bioscience business early in 2011 arising out of our plant consolidations, temporary weakness in the LED markets and production capacity constraints in Hitech. We expect Hitech capacity to start ramping up beginning in Q2 2012 with the opening of a new plant in Taiwan. A reconciliation of reported to adjusted (organic) sales can be found on page 10.

The adjusted operating income margin in the first quarter of 2012 was 26.6% of sales compared to 26.9% of sales in the first quarter of 2011. The benefit to operating margins from the higher sales levels was offset primarily by higher amortization of intangible assets related to our recent acquisitions. Amortization of acquisition related intangibles amounted to $6 million, or $0.03 per diluted share in the first quarter of 2012 compared to $3 million or $0.02 per diluted share in the first quarter of 2011. First quarter 2012 adjusted operating income excludes $5 million, or $0.03 per diluted share, of one-time transaction costs associated with our recent acquisitions of BioReliance and Research Organics. A reconciliation of reported to adjusted operating income and margin is provided on page 11.

The effective tax rate for the first quarter of 2012 was 32% compared to 28% in the first quarter of 2011. The first quarter 2011 tax rate included a benefit from the resolution and related release of certain tax contingencies amounting to $0.04 per diluted share. The effective tax rate for all of 2012 is expected to be approximately 30% to 31% of pretax income.

Free cash flow (defined on page 9) for the first quarter of 2012 was $112 million, compared to $133 in the first quarter of 2011. Higher capital spending primarily associated with the completion of new facilities in the U.S and Asia-Pacific region and higher uses of cash for working capital to support sales growth were the primary drivers for the lower free cash flow. A reconciliation of net cash provided by operating activities to free cash flow is provided on page 11.

Other highlights include:

2012 OUTLOOK:

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OTHER INFORMATION:

Cash Flow and Debt: Net cash provided by operating activities for the first quarter of 2012 was $144 million compared to $151 million for the first quarter of 2011. Higher use of cash for working capital to support higher sales levels was the primary contributor to the decline in operating cash flow. Capital expenditures were $32 million in the first quarter of 2012 compared to $18 million in the first quarter of 2011. Free cash flow of $112 million for the first quarter of 2012, $193 million of short-term debt and the partial use of cash on hand were used to fund $389 million of acquisitions, pay $24 million in dividends and return $25 million to shareholders through share repurchases. The Company’s debt to capital ratio was 24% at March 31, 2012 and 19% at December 31, 2011.

Share Repurchases: We acquired 0.4 million shares in the first quarter of 2012 at an average share price of $71.86. There were 121 million shares outstanding at March 31, 2012. The Company expects to continue to offset the dilutive impact of issuing share based incentive compensation with future repurchases, the timing and amount of which will depend upon market conditions and other factors.

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Cautionary Statement: This release contains forward-looking statements. Such statements involve risk and uncertainty, including financial, business environment and projections, and relate to matters that are not historical facts. Such statements are preceded by, followed by or include the words “believes,” “can,” “expects,” “plans,” “anticipates,” “should,” “enhances,” “estimates,” “forecasts,” “will” or similar expressions. Additionally, this release contains forward-looking statements relating to future performance, goals, strategic actions and initiatives and similar intentions and beliefs, including, without limitation, statements with respect to the Company’s expectations, goals, beliefs, intentions, outlook, plans and the like regarding future sales, earnings, return on equity, cost savings, process improvements, free cash flow, share repurchases, capital expenditures, acquisitions and other matters. These statements are based on assumptions regarding Company operations, investments and acquisitions and conditions in the markets the Company serves. The Company believes these assumptions are reasonable and well founded. Such statements in this release are subject to risks and uncertainties, including, among others, certain economic, political and technological factors. Actual results could differ materially from those stated or implied in this release due to such factors as (1) global economic conditions, (2) changes in pricing and the competitive environment and the global demand for the Company’s products, (3) fluctuations in foreign currency exchange rates, (4) changes in research funding and the success of research and development activities, (5) failure of planned sales initiatives in our Research and SAFC business units, (6) dependence on uninterrupted manufacturing operations and global supply chain, (7) changes in the regulatory environment in which the Company operates, (8) changes in worldwide tax rates or tax benefits from domestic and international operations, including the matters described in Note 10 – Income Taxes, to the Company’s consolidated financial statements included in Item 8, Part II in the Company’s Annual Report on Form 10-K for the year ended December 31, 2011 (the “10-K”), (9) exposure to litigation, including product liability claims, (10) the ability to maintain adequate quality standards, (11) reliance on third party package delivery services, (12) an unanticipated increase in interest rates, (13) other changes in the business environment in which the Company operates, (14) the outcome of the outstanding matters described in Note 11 – Contingent Liabilities and Commitments, to the Company’s consolidated financial statements included in Item 8, Part II in the 10-K and (15) acquisitions or divestitures of businesses. A further discussion of the Company’s risk factors can be found in Item 1A of Part I of the 10-K. The Company does not undertake any obligation to update these forward-looking statements.

About Sigma-Aldrich: Sigma-Aldrich is a leading Life Science and High Technology company whose biochemical, organic chemical products, kits and services are used in scientific research, including genomic and proteomic research, biotechnology, pharmaceutical development, the diagnosis of disease and as key components in pharmaceutical, diagnostics and high technology manufacturing. Sigma-Aldrich customers include more than one million scientists and technologists in life science companies, university and government institutions, hospitals and industry. The Company operates in 40 countries and has nearly 9,000 employees whose objective is to provide excellent service worldwide. Sigma-Aldrich is committed to accelerating customer success through innovation and leadership in Life Science, High Technology and Service. For more information about Sigma-Aldrich, please visit its website, at www.sigma-aldrich.com.

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Non-GAAP Financial Measures: The Company supplements its disclosures made in accordance with accounting principles generally accepted in the United States (i.e., U.S. GAAP) with certain non-GAAP financial measures. The Company does not, and does not suggest investors should, consider such non-GAAP financial measures in isolation from, or as a substitute for, GAAP financial information. These non-GAAP measures may not be consistent with the presentation by similar companies in the Company’s industry. Whenever the Company uses such non-GAAP measures, it provides a reconciliation of such measures to the most closely applicable GAAP measure. See the Supplemental Financial Information on pages 10 and 11 for these reconciliations.

With over 60% of sales denominated in currencies other than the U.S. dollar, management uses currency adjusted sales growth when analyzing Company performance, and believes it is useful as well to investors to judge the Company’s performance. Organic sales growth data presented in this release excludes currency and acquisitions impacts. The Company calculates the impact of changes in foreign currency exchange rates by multiplying current period activity by the difference between current period exchange rates and prior period exchange rates. The result is the defined impact of “changes in foreign currency exchange rates.” While we are able to report past currency impacts, we are unable to estimate changes that may occur later in 2012 to applicable exchange rates. Any significant changes in currency exchange rates would likely have a significant impact on reported growth rates due to the volume of sales denominated in foreign currencies.

Management also uses the following non-GAAP measures to judge its performance and ability to pursue opportunities that enhance shareholder value: adjusted net income and EPS; adjusted operating income margin (reconciled on page 11); and free cash flow (defined on page 9). Due to the uncertain timing of future restructuring and other special charges we are unable to include these charges in the 2012 diluted adjusted EPS forecast or provide reconciliation to the corresponding GAAP measures. Management believes this non-GAAP information is useful to investors as well.

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SIGMA-ALDRICH CORPORATION

Consolidated Statements of Income (Unaudited)

(in millions except per share amounts)

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SIGMA-ALDRICH CORPORATION

Consolidated Balance Sheets (Unaudited)

(in millions)

8

SIGMA-ALDRICH CORPORATION

Consolidated Statements of Cash Flows (Unaudited)

(in millions)

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SIGMA-ALDRICH CORPORATION

Supplemental Financial Information - (Unaudited)

Sales Growth by Business Unit

Business Unit Sales

(in millions)

10

SIGMA-ALDRICH CORPORATION

Supplemental Financial Information - (Unaudited)

Reconciliation of Reported net income to Adjusted net income

Income Statement Ratios

Reconciliation of Reported Operating Income to Adjusted Operating Income

Reconciliation of Reported Operating Income Margin to Adjusted Operating Income Margin

Reconciliation of Free Cash Flow

(in millions)

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