Sepracor Inc. and Eisai Co. Ltd. Announce Partnership for Development and Commercialization of LUNESTA(R) in Japan.

* Collaboration is the first partnership for expansion of the LUNESTA([R]) brand eszopiclone franchise outside of U.S.

* Eisai to complete development of eszopiclone in Japan and will have exclusive marketing rights to the product for the Japanese market

* Submission of Japanese marketing application targeted for 2010/2011

* Japanese insomnia market estimated at approximately $500 million in 2006

MARLBOROUGH, Mass. -- Sepracor Inc. (Nasdaq: SEPR) today announced an agreement with Eisai Co. Ltd. for the development and commercialization of Sepracor's eszopiclone product, which is known in the U.S. by the brand name LUNESTA, for the Japanese market. Under the agreement, Eisai will be responsible for completing the remaining clinical trials necessary for attaining marketing approval from the Japanese regulatory authorities, and contingent on regulatory approval, commercialization of the product in Japan. Sepracor anticipates that the Japanese marketing application will be submitted in 2010/2011. In exchange, Sepracor is entitled to receive an initial milestone payment and subsequent payments upon accomplishment of various development, regulatory and pricing milestones, as well as royalties on product sales and compensation for providing the product's active ingredient.

"Eisai is one of Japan's largest and most respected pharmaceutical companies, and we are delighted to have established this partnership with such a well-regarded company," said Adrian Adams, President and Chief Executive Officer of Sepracor. "Eisai's long-proven development, especially in the central nervous system therapeutic area, and commercialization infrastructure, provides an optimal launch platform from which to expand our LUNESTA franchise to the Japanese insomnia market. This milestone event is reflective of our overall global corporate strategy to fully leverage our product franchises while driving enhanced research and development productivity and successfully pursuing aligned and value-enhancing corporate development and licensing initiatives."

LUNESTA has been commercially available in the U.S. since 2005 for the treatment of insomnia and had product revenues of approximately $566.8 million in 2006. In 2006, the sedative hypnotic market in Japan was approximately $500 million. An estimated 24 million people in Japan experience insomnia, but only 7 to 8 million are being treated.

About Sepracor

Sepracor Inc. is a research-based pharmaceutical company dedicated to treating and preventing human disease by discovering, developing and commercializing innovative pharmaceutical products that are directed toward serving unmet medical needs. Sepracor's drug development program has yielded a portfolio of pharmaceutical products and candidates with a focus on respiratory and central nervous system disorders. Currently marketed products include LUNESTA brand eszopiclone, XOPENEX([R]) brand levalbuterol HCl Inhalation Solution, XOPENEX HFA([R]) brand levalbuterol tartrate Inhalation Aerosol and BROVANA([TM]) brand arformoterol tartrate Inhalation Solution. Sepracor's corporate headquarters are located in Marlborough, Massachusetts.

About Eisai

Eisai Co. Ltd. was founded in Japan in 1941 and has operations in the U.S., Europe and Asia. Eisai is a human health care (hhc) company that seeks to discover and develop innovative therapies that can satisfy unmet medical needs and contribute to the health and well-being of people worldwide. Eisai's hhc mission is to focus on patients and their families as the most important participants in the health care process, and the company is dedicated to improving their lives. Eisai's product focus is principally on treatments for central nervous system diseases and gastrointestinal disorders, and they are promoted by approximately 3,500 sales representatives worldwide. The company currently commercializes ARICEPT([R]) (donepezil hydrochloride tablets), ACIPHEX([R]) (rabeprazole sodium tablets), CEREBYX([R]) (fosphenytoin sodium injection), ZONEGRAN([R]) (zonisamide capsules) and FRAGMIN([R]) (dalteparin sodium injection), for the U.S. market.

Forward-Looking Statement 

This news release contains forward-looking statements that involve risks and uncertainties, including statements with respect to the safety, efficacy and potential benefits of LUNESTA; timing and success of regulatory filings in Japan and the development and commercialization of eszopiclone in the Japanese market; Sepracor's ability to leverage its product franchises and enter into additional corporate development and licensing arrangements; the market for insomnia products in Japan; and future payments to Sepracor. Among the factors that could cause actual results to differ materially from those indicated by such forward-looking statements are: unexpected delays in the development and commercialization of eszopiclone for the Japanese market; Sepracor's ability to successfully collaborate with Eisai; the performance of Eisai and Sepracor's other licensees and collaboration partners and its ability to enter into new licenses and collaborations; the clinical benefits and safety of eszopiclone; changes in the use and/or label of LUNESTA in the U.S.; the scope of Sepracor's patents and the patents of others and the success of challenges by others of Sepracor's patents; and certain other factors that may affect future operating results that are detailed in the company's quarterly report on Form 10-Q for the quarter ended March 31, 2007 filed with the Securities and Exchange Commission.

In addition, the statements in this press release represent Sepracor's expectations and beliefs as of the date of this press release. Sepracor anticipates that subsequent events and developments may cause these expectations and beliefs to change. However, while Sepracor may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Sepracor's expectations or beliefs as of any date subsequent to the date of this press release.

Brovana is a trademark and Lunesta, Xopenex and Xopenex HFA are registered trademarks of Sepracor Inc. Aricept and Aciphex are registered trademarks of Eisai Co. Ltd. Cerebyx is a registered trademark of Warner-Lambert Company. Zonegran is a registered trademark of Dainippon Sumitomo Pharma Co., Ltd. Fragmin is a registered trademark of Pfizer Health AB Corporation.

For a copy of this release or any recent release, visit Sepracor's web site at www.sepracor.com.