A three-day rally is ending much like it began, with a steep and sudden turn.
Stocks started higher early Thursday but turned lower within 20 minutes. Indexes in the U.S. and Europe sank after Germany's main stock index suddenly lost 4 percent. Traders were at a loss to explain the move.
The Dow fell 171 points, or 1.5 percent, to close at 11,150. The S&P 500 index fell 18 points, or 1.6 percent, to 1,159. The Nasdaq fell 48 points, or 2 percent, to 2,420.
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.