Merger news and analyst upgrades were some of the catalysts behind the most actively traded stocks on Monday.
Shares of Yahoo fell in heavy trading Monday after news reports suggested the Internet company was no longer in merger talks with Microsoft.
Alcan shares surged more than 30% after rival alumnium producer Alcoa submitted a hostile takeover bid of $26.9 billion in a cash-and-stock deal. Canada-based Alcan said it was considering the unsolicited offer, which would create the world's largest aluminum company.
Shares of Armor Holdings rose more than 5% after British defense contractor BAE Systems moved to expand its share of the U.S. military market on Monday with a $4.1 billion deal to buy the body armor and Army truck maker.
Bear Stearns upgraded Darden Restaurants to "outperform" after the company said it would close 56 of its Smokey Bones Barbeque & Grill restaurants, and sell the remaining 73, prompting a 4% rise in share price. The restaurant operator's new stance removes a drag on earnings and a major management distraction and adds more debt leverage, Bear Stearns said.
A trade magazine said Wal-Mart Stores may be interested in acquiring Gottschalks, sending shares of the latter up 4%. Wal-Mart could be looking to step up its presence in California, Women's Wear Daily reported on Monday.
Shares of Ohio Casualty surged 30% after Liberty Mutual Group said it would acquire the company for $44 per share in cash, or $2.7 billion.
Abbott Laboratories gained 1% after Lehman Brothers raised its rating on the stock to "overweight" from "equal-weight."