NxStage Medical Inc has entered into a definitive agreement to acquire Medisystems Corp for 6.5 million shares of NxStage common stock, valued at approximately $78.7 million.

The manufacturer of the NxStage System One portable kidney dialysis machine has been a business partner with the medical device distributor for 7 years. Medisystems manufactures the cartridge used in the NxStage System One, as well as other devices used in dialysis and blood related treatments.

The transaction is subject to the approval of NxStage’s shareholders, as well as customary closing conditions and anti-trust approvals, including expiration of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. The transaction is expected to close in the last quarter of 2007.