Danaher Corp. on Monday said that it signed an agreement to buy Chatsworth medical test maker Iris International Inc. in a deal worth about $341 million.

Iris makes automated in-vitro diagnostics systems and related products. Danaher, a Washington, D.C. conglomerate that wants to expand in the medical diagnostics business, said it will pay $19.50 for each share of Iris, a 45 percent premium over the Iris’ closing stock price of $13.42 on Friday.

Based on Iris’ 17.5 million shares outstanding, the deal is worth about $341 million. The companies valued the deal, which is expected to close in the fourth quarter, at about $338 million, including assumed cash and debt.

Iris shares jumped $6.03, or 45 percent, to $19.45 in morning trading on the Nasdaq.