GlaxoSmithKline (NYSE: GSK) is investing $129 million in respiratory drug development firm Theravance (Nasdaq: THRX).

GSK, which maintains its U.S. headquarters in the Triangle, said Monday it would buy 5.75 million shares of Theravance at $22.50 per share. The deal will increase GSK’s holdings in Theravance to 19 percent of its outstanding shares.

Over the past five trading days, Theravance has traded at an average price of $22.35. Shares closed Friday at $22.85. Theravance’s share price has nearly doubled since September and traded under $10 in February.

The two companies have worked since 2002.

“We were keen to take advantage of this opportunity to increase our shareholding in Theravance,” said Moncef Slaoui, chairman of research and development at GSK, in a statement. “This reflects the confidence we have in the Relovair programme and the wider late stage respiratory pipeline that we have built up through the collaboration.”

Read the full statement here.

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