Swiss pharmaceuticals group Roche has made a fresh bid to buy United States-based Genentech by offering $86.50 (SFr100) per share directly to shareholders.
Friday's offer by Roche, which already owns 55.8 per cent of Genentech, comes after its earlier offer of $89 per share was rejected as too low by the San Francisco-based company's board in July.
The new offer values the outstanding shares at $42.1 billion, about $1.6 billion less than the previous bid.
Genentech shares closed at $84.09 on Thursday on the New York Stock Exchange. The stock has traded between $66.80 and $99.14 over the past 52 weeks.
Roche said its new offer is aimed directly at shareholders, bypassing the board.
"We feel it is now time to give the Genentech minority shareholders the opportunity to decide on our offer," Roche chairman Franz Humer said in a statement.
"Especially in the current market environment the offer provides an opportunity for all public shareholders to achieve liquidity and to receive a fair price for all their shares."
Roche said it intends to retain Genentech's San Francisco base as an independent research centre if the takeover succeeds.