Swiss pharmaceutical giant Roche is to acquire United States diagnostics firm Ventana for $3.4 billion (SFr3.77 billion).

Roche and Ventana Medical Systems signed a definitive agreement under which Roche will increase the purchase price in its tender offer from $75 to $89.50 per share.

Ventana's board of directors, which had previously rejected Roche's advances, will recommend that shareholders accept the offer, according to a joint statement from both companies on Tuesday.

In late June 2007, Roche made an unsolicited cash offer to buy all of the Arizona company's common shares outstanding but Ventana resisted the approach, deeming the price "inadequate". The final agreed price represents an increase of 19 per cent on the initial offer.

Headquartered in Basel, Roche is one of the world's largest research-focused healthcare groups in the fields of pharmaceuticals and diagnostics.

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