Stocks in the United States fell in choppy trade on Monday as shares of the big drugmakers fell despite a $US41 billion takeover being proposed by Merck with Schering-Plough.
Merck was down 7.7% at $US20.99, Johnson & Johnson shed 2.9% to $US46.60 and Pfizer slipped 0.8% to $US12.63. Schering-Plough rose 14.2% to $US20.13.
The Dow Jones industrial average dropped 79.89 points, or 1.21%, to 6,547.05.
Standard & Poor's 500 Index fell 6.85 points, or 1%, to 676.53. The Nasdaq Composite Index slid 25.21 points, or 1.95%, to 1,268.64 - its lowest close since October 2002.
Google's stock fell 5.7% to $US290.89.
However, financial stocks rose as Federal Reserve Chairman Ben Bernanke attended a meeting on the US economy with President Barack Obama.
Shares of Bank of America rose 19.4% to $US3.75 and Wells Fargo & Co jumped almost 16% to $US9.97.
In an interview on CNBC television, billionaire investor Warren Buffett said that the current environment was an "economic Pearl Harbor."
But he added investors will do "considerably better owning a group of equities" rather than US Treasury securities over a 10-year period.
Trading was moderate on the New York Stock Exchange, with about 1.56 billion shares changing hands - slightly above last year's estimated daily average of 1.49 billion.
About 2.06 billion shares were traded on the Nasdaq - below last year's daily average of 2.28 billion.