The ball is in Baxter’s court, again.

Baxter International Inc.’s $3.8 billion offer for National Medical Care, W.R. Grace & Co.’s kidney dialysis business, was rejected over the weekend as Grace chose instead to combine the unit with a third company.

Grace’s decision blew apart Baxter’s strategy. The health care giant made its offer public last Friday in an effort to force the issue.

Grace agreed to combine National Medical with the dialysis unit of Germany’s Fresenius AG, a deal that will yield $2.3 billion for Grace and allow it to retain a stake in the business.