Stock indexes fell sharply soon after trading began Thursday and then bounced around near their bottoms the rest of the day, ending a three-day rally.
Indexes in both the U.S. and Europe sank after Germany's main stock index, the DAX, suddenly dipped 4 percent. Traders struggled to explain the dive. The Dow Jones industrial average closed down 170.89 points, or 1.5 percent, to close at 11,149.82. It had been up 85 points the first few minutes of trading.
Bank of America Corp. jumped 9 percent on news that Warren Buffett will invest $5 billion in the troubled bank. BofA had lost half its value this year as investors worried about its need to raise capital and its growing liabilities related to subprime mortgages. BofA stock was up 26 percent early, to $8.80, and closed at $7.65, up 66 cents.
Other banks also rose after the billionaire investor gave his backing to Bank of America. Morgan Stanley gained 2.7 percent and Citigroup Inc. 4.8 percent. BofA and American Express Co. were the only two of the 30 companies in the Dow to rise.
This week's trading has been marked by a series of sudden reversals. Robert Stein, a money manager responsible for $1.2 billion at Astor Asset Management, said questions about the economy have made investors uncertain and the stock market more volatile. Gains made one day have disappeared the next, or even in the same day.
"We're not seeing anything that's convincingly bearish enough to call another recession, but nothing optimistic enough to suggest that a recovery is going to regenerate," Stein said.
Friday could be another day of big swings as Federal Reserve Chairman Ben Bernanke gives a highly anticipated speech at a conference in Jackson Hole, Wyo. Bernanke speaks at 10 a.m. EDT.
Earlier Thursday, the government reported an increase in the number of people applying for unemployment benefits last week. The Labor Department said applications rose to 417,000, the highest in five weeks, but the figure was inflated by a strike at Verizon that earlier this week.
The S&P 500 index fell 18.33 points, or 1.6 percent, to 1,159.27. The Nasdaq fell 48.06 points, or 1.9 percent, to 2,419.63.
The S&P, the benchmark for most money managers, has gained 3 percent this week but is still down 10 percent for the month. Thursday's drop broke a three-day rally in which the Dow gained 503 points.
Paul Zemsky, chief investment officer of ING Investment Management in New York, said this week's gains were a result of investors bargain-hunting after stocks fell too far over the past month. He also said some of the gains were caused by technical trading as investors bought shares to exit short positions, or bets that the market would continue to fall.
Zemsky expects to see more big swings as long as the fear of recession hangs over the market. "People are trying to adjust their positions to news," he said. "Once it's clear where the economy is headed, I think things will calm down."
There's plenty of speculation about whether Bernanke will offer more support for the economy. It was at the same conference last year that he laid out an argument for what became a $600 billion bond-buying program by the central bank.
Zemsky thinks there's little chance Bernanke will announce any action Friday. "There's nothing more than hope that Bernanke will drop a gift from the sky."
More than three stocks fell for every one that rose on the New York Stock Exchange. Trading volume was above average at 5 billion shares, thanks to BofA, which accounted for nearly 900 million shares.