Traders are looking past a surprisingly strong report on the U.S. jobs market, focusing instead on Europe's spreading debt crisis and Thursday's brief plunge of nearly 1,000 points in the Dow Jones industrials.
Stock prices were fluctuating sharply, paring some of their earlier losses.
In midday trading the Dow was off 67.71, or 0.6 percent, to 10,452.61.
The Standard & Poor's 500 index fell 9.28, or 0.8 percent, to 1,118.87, while the Nasdaq composite fell 30.39, or 1.3 percent, to 2,289.25.
Falling stocks outpaced gainers by about three to one on the New York Stock Exchange, where volume was a heavy 1 billion shares.
