But analysts said Roche might need to pay more, and investors seemed to agree by bidding Genentech's share price above the offer.
Roche Holdings AG already owns 55.9 percent of the South San Francisco, Calif.-based drugmaker. It offered $89 per share, 8.8 percent above Genentech's closing price Friday and 19 percent above the price a month ago.
Genentech shares climbed well above that offer in midday trading on Monday, jumping $10.58, or 12.9 percent, to $92.40 after rising to a 52-week high of $94.19 earlier in the session -- a bet that the bidding will go higher.
The California company took no position on the offer, but confirmed in a statement that a special committee of its board would meet promptly to decide on a response.
Roche shares fell 4.8 percent to close at 171.00 francs ($167.27) on Monday on the Zurich exchange. The offer came as Roche announced a 2 percent decline in its first half net profit.
The weak U.S. dollar makes American assets cheaper for foreigners, a factor in the proposed $52 billion takeover of U.S. brewer Anheuser-Busch Cos. by Belgian-based multinational InBev SA. The dollar is sagging under U.S. subprime mortgage crisis woes, a big trade deficit, and interest rate cuts by the U.S. Federal Reserve.
"The timing has a lot to do with the weak dollar," said Beatrice Kunz, analyst with Clariden Leu. "It's not only the currency but the currency is helping."
Kunz said the Roche stock weakness indicated that Roche might have to increase the price to ultimately get the deal done. "Investors doubt whether they get it for this $89 (per share) and maybe the company is trying to get a better price," she said. "But I don't think the better price is coming from another company."
The U.S. dollar has been plunging in recent years against the Swiss franc and the euro. In 2000 the dollar was worth 1.82 francs, but by end of last year it had dropped 1.25 francs. In March, it fell below 1-to-1 before rising above parity, where it has been hovering since. On Monday it was 1.02 francs to the dollar. In 1971, the U.S. dollar was worth four francs.
The company said its earlier investment in Genentech had helped the biotechnology company focus on innovation and long-term projects, "leading to some of the most important breakthroughs in the treatment of cancer and other life-threatening diseases."
Roche codevelops and markets Genentech products outside North America. It said the takeover would "accelerate the search for new solutions for unmet medical needs."
"The combined entity will be the seventh largest U.S. pharmaceuticals company in terms of market share," Roche said in a statement from its Basel headquarters. "It will generate more than $15 billion in annual revenues."
Franz Humer, Roche board chairman, indicated there would be job cuts but did not say how many. About 10,700 people work for Genentech.
The takeover offer is the largest ever made by a Swiss concern.
Global Insight analyst Gaelle Marinoni said 8.8 percent above the closing price Friday was not a big premium but as Roche already owned the majority of shares, the offer was "probably fair."
Minority shareholders "might try to get a little more," she said.
Lazard Capital Markets said the buyout could take awhile.
"In our opinion, if a transaction takes place, it likely would be at a higher price," it said.
Roche said its first half net profit declined to 5.7 billion Swiss francs ($5.6 billion) in view of a weaker U.S. dollar and a sharp drop in government purchases of the anti-viral Tamiflu because anti-pandemic stockpiles have been filling up. Net income was down from 5.9 billion francs for the year earlier period.
Roche reports profit figures only for the first six months and full year. Sales were 20 billion francs ($19.6 billion), down 4 percent from the first half of 2007.
"Our long and successful participation in Genentech has provided great benefits to both of our companies and shareholders. It has resulted in one of the biggest success stories in the healthcare industry," said Humer.
Roche said the takeover would result in improved operational efficiency by reducing complexity, eliminating duplications and increasing scale in the United States.
Humer said Roche's investment in Genentech over the years has helped it to focus on innovation and long-term projects, leading to some of the most important breakthroughs in the treatment of cancer and other life-threatening diseases.
"Combining the strengths of Roche and Genentech will create significant value and result in benefits for patients, employees and shareholders," he said.
Roche said Genentech's South San Francisco site would operate as an independent research and early development center and become headquarters of combined U.S. commercial operations.
The announcement said the Genentech board of directors will establish a committee of independent directors to evaluate Roche's proposal with the assistance of independent outside financial and legal advisers.
Genentech board members who are employees of Roche will not participate in the evaluation of the proposal, it said.
The statement said Roche plans to combine Genentech and a Roche subsidiary and that all currently outstanding shares and options of Genentech other than shares owned by Roche would be converted into cash.
Precise terms will be determined through negotiations with the independent directors, it said, adding that it expects the deal would be subject to the approval of holders of a majority of the Genentech outstanding shares not held by Roche.