Exhibit 99.1

				Repligen Corporation 41 Seyon Street Building #1, Suite 100 Waltham, Massachusetts 02453

Repligen Reports First Quarter 2018 Financial Results

WALTHAM, MA – May 8, 2018 – Repligen Corporation (NASDAQ:RGEN), a life sciences company focused on bioprocessing technology leadership, today reported financial results for its first quarter ended March 31, 2018. Provided in this press release are financial highlights for the quarter, updates to our financial guidance for the year 2018 and access information for today’s webcast and conference call.

Tony J. Hunt, President and Chief Executive Officer said, “We had a strong start to the year led by sales of our direct filtration and chromatography products, which were up by over 90% year-on-year. This includes our Spectrum business, which continues to outperform our expectations. We are also excited about the depth of our R&D pipeline which is generating new products, including our recently launched OPUS 80R pre-packed columns that address late stage clinical and commercial opportunities. Our end markets remain strong and with robust demand for our single-use and flexible bioprocessing technologies, we are raising our revenue guidance for 2018.”

First Quarter 2018 Snapshot

Financial Details for the First Quarter of 2018

REVENUE

GROSS PROFIT and GROSS MARGIN

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OPERATING INCOME and OPERATING MARGIN

NET INCOME

EARNINGS PER SHARE

EBITDA

CASH

All reconciliations of GAAP to adjusted (non-GAAP) figures above, as well as EBITDA to adjusted EBITDA, are detailed in the reconciliation tables included later in this press release.

Financial Guidance for 2018

Our financial guidance for the year 2018 is based on expectations for our existing business and does not include the financial impact of potential new acquisitions or future fluctuations in foreign currency exchange rates. This guidance includes the first full year of sales from our acquisition of Spectrum Inc. on August 1, 2017. The guidance below includes revisions to the full year 2018 guidance that we provided on February 22, 2018. Our current expectations for gross margin, operating income and income tax rate guidance are consistent with our previous guidance.

YEAR 2018 GUIDANCE UPDATES:

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Our non-GAAP guidance for the year 2018 excludes the following items:

Our non-GAAP guidance for the year 2018 includes:

All reconciliations of GAAP to adjusted (non-GAAP) guidance are detailed in the tables included later in this press release.

Conference Call

Repligen will host a conference call and webcast today, May 8, 2018, at 8:30 a.m. EST, to discuss first quarter of 2018 financial results and corporate developments. The conference call will be accessible by dialing toll-free (866) 777-2509 for domestic callers or (412) 317-5413 for international callers. No passcode is required for the live call. In addition, a webcast will be accessible via the Investor Relations section of the Company’s website. Both the conference call and webcast will be archived for a period of time following the live event. The replay dial-in numbers are (877) 344-7529 from the U.S., (855)-669-9658 from Canada and (412) 317-0088 for international callers. Replay listeners must provide the passcode 10120055.

Non-GAAP Measures of Financial Performance

To supplement our financial statements, which are presented on the basis of U.S. generally accepted accounting principles (GAAP), the following non-GAAP measures of financial performance are included in this release: revenue growth rate at constant currency, adjusted gross profit and adjusted gross margin, adjusted income from operations and adjusted operating margin, earnings before interest, taxes, depreciation and amortization (EBITDA), adjusted EBITDA, adjusted net income and adjusted earnings per diluted share (EPS). The Company provides revenue growth rates in constant currency to exclude the impact of foreign currency translation in order to facilitate a comparison of its current revenue performance to its past revenue performance. To calculate revenue growth rates in constant currency, the Company converts actual net sales from local currency to U.S. dollars using constant foreign currency exchange rates in the current and prior period.

The Company’s non-GAAP financial results and/or non-GAAP guidance exclude the impact of: acquisition costs related to the Company’s acquisitions of Atoll GmbH, TangenX Technology Corporation, and Spectrum Lifesciences, LLC (formerly known as Spectrum, Inc., inventory step-up charges related to the

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acquisition of Spectrum, intangible amortization costs, non-cash interest expense, and in the case of EBITDA, cash interest expense related to the Company’s May 2016 convertible debt issuance. Also excluded are tax benefits associated with valuation allowances on deferred tax assets, the impact on tax of intangible amortization, tax benefits associated with variable integration expenses and tax benefits associated with tax reform. These costs are excluded because management believes that such expenses do not have a direct correlation to future business operations, nor do the resulting charges recorded accurately reflect the performance of our ongoing operations for the period in which such charges are recorded.

A reconciliation of GAAP to adjusted non-GAAP financial measures is included as an attachment to this press release. When analyzing the Company’s operating performance and guidance investors should not consider non-GAAP measures as substitutable for the comparable financial measures prepared in accordance with GAAP.

About Repligen Corporation

Repligen Corporation (NASDAQ:RGEN) is a global bioprocessing company that develops and commercializes highly innovative products that deliver cost and process efficiencies to biological drug manufacturers worldwide. Our portfolio includes protein products (Protein A affinity ligands, cell culture growth factors), chromatography products (OPUS^® pre-packed columns, chromatography resins, ELISA kits) and filtration products (including XCell™ ATF systems, TangenX™ Sius™ flat sheet TFF cassettes, and Spectrum KrosFlo™ hollow fiber TFF cartridges and systems). The Protein A ligands and growth factor products that we produce are essential components of Protein A affinity resins and cell culture media, respectively. Protein A affinity resins are the industry standard for downstream separation and purification of monoclonal antibody-based therapeutics. Our growth factors are used in upstream processes to accelerate cell growth and productivity in a bioreactor. Our innovative line of OPUS^® chromatography columns, used in downstream processes for bench-scale through clinical-scale purification needs, are delivered pre-packed to our customers with their choice of resin. Our XCell™ ATF Systems, available in stainless steel and single-use configurations, are used upstream to continuously eliminate waste from a bioreactor, to concentrate cells and increase product yield. Single-use Sius™ TFF cassettes and hardware are used for biologic drug concentration in downstream filtration processes. Spectrum KrosFlo™ TFF cartridges and systems are used in both upstream and downstream filtration processes. Repligen’s corporate headquarters are in Waltham, MA (USA), with additional administrative and manufacturing operations in Shrewsbury, MA, Rancho Dominguez, CA, Lund, Sweden and Ravensburg, Germany.

The following constitutes a “Safe Harbor” statement under the Private Securities Litigation Reform Act of 1995: This press release contains forward-looking statements, which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Investors are cautioned that statements in this press release which are not strictly historical statements, including, without limitation, express or implied statements or guidance regarding current or future financial performance and position, including cash and investment position, demand in the markets in which we operate, the expected performance of the Spectrum business or our integration of Spectrum, management’s strategy, plans and objectives for future operations or acquisitions, product development and sales, selling, general and administrative expenditures, intellectual property, development and manufacturing plans, availability of materials and product and adequacy of capital resources and financing plans constitute forward-looking statements identified by words like “believe,” “expect,” “may,” “will,” “should,” “seek,” “anticipate,” or “could” and similar expressions. Such forward-looking statements are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated, including, without

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limitation, risks associated with: our ability to successfully grow our bioprocessing business, including as a result of acquisition, commercialization or partnership opportunities; our ability to successfully integrate any acquisitions, our ability to develop and commercialize products and the market acceptance of our products; reduced demand for our products that adversely impacts our future revenues, cash flows, results of operations and financial condition; our ability to compete with larger, better financed bioprocessing, pharmaceutical and biotechnology companies; our compliance with all Food and Drug Administration and EMEA regulations; our volatile stock price; and other risks detailed in Repligen’s most recent Annual Report on Form 10-K on file with the Securities and Exchange Commission and the other reports that Repligen periodically files with the Securities and Exchange Commission. Actual results may differ materially from those Repligen contemplated by these forward-looking statements. These forward looking statements reflect management’s current views and Repligen does not undertake to update any of these forward-looking statements to reflect a change in its views or events or circumstances that occur after the date hereof except as required by law.

Repligen Contact:

Sondra S. Newman

Senior Director Investor Relations

(781) 419-1881

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REPLIGEN CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

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REPLIGEN CORPORATION

RECONCILIATION OF GAAP INCOME FROM OPERATIONS TO

NON-GAAP (ADJUSTED) INCOME FROM OPERATIONS

(Unaudited)

REPLIGEN CORPORATION

RECONCILIATION OF GAAP NET INCOME TO NON-GAAP (ADJUSTED) NET INCOME

(Unaudited)

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REPLIGEN CORPORATION

RECONCILIATION OF GAAP NET INCOME PER SHARE TO

NON-GAAP (ADJUSTED) NET INCOME PER SHARE

(Unaudited)

Totals may not add due to rounding.

REPLIGEN CORPORATION

RECONCILIATION OF GAAP NET INCOME TO ADJUSTED EBITDA

(Unaudited)

8

REPLIGEN CORPORATION

RECONCILIATION OF GAAP COST OF SALES TO NON-GAAP (ADJUSTED) COST OF SALES

(Unaudited)

REPLIGEN CORPORATION

RECONCILIATION OF GAAP SG&A EXPENSE TO NON-GAAP (ADJUSTED) SG&A EXPENSE

(Unaudited)

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REPLIGEN CORPORATION

RECONCILIATION OF GAAP NET INCOME GUIDANCE TO

ADJUSTED (NON-GAAP NET INCOME GUIDANCE)

REPLIGEN CORPORATION

RECONCILIATION OF GAAP NET INCOME PER SHARE GUIDANCE TO

ADJUSTED (NON-GAAP) NET INCOME PER SHARE GUIDANCE

Totals may not add due to rounding.

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