Roche has started a cash tender offer for all of Genentech's publicly-held outstanding shares, it emerged this week.
It already owns about 55.8 per cent of the shares but has now bid for the rest, with the offer and withdrawal rights scheduled to end on March 12th 2009.
The price tendered by Roche is $86.50 (58.40 pounds) per share, which is less than the original proposal made last July of $89 by way of a negotiated merger.
The latest offer has been made directly to the shareholders of Genentech after its board of directors' special committee rejected 2008's public proposal.
Roche group chairman Franz Humer said the company plans to "nurture" the science-driven environment of its potential purchase.
"Genentech's research and early development will operate as an independent unit," he explained. "We remain committed to retaining Genentech's top talent and approach to discovering and progressing new medicines."
Last week saw Roche announce "strong" operating figures for 2008.
It confirmed double-digit sales growth and a dividend increase of nine per cent.See all the latest jobs in Pharmaceutical