Several companies fell Thursday after reporting weak earnings.
Harman International, which makes audio systems for cars, Varian Medical Systems and Celgene all dropped in midday trading Thursday after their revenue fell short of analysts' estimates.
The Dow Jones industrial average lost 78 points, or 0.4 per cent, to 17,956 as of 11:45 a.m. Eastern time.
The Standard & Poor's 500 index fell 10 points, or 0.5 per cent, to 2,096. The Nasdaq composite fell 45 points, or 0.9 per cent, to 4,977.
Bond prices fell after some mostly encouraging news on the U.S. economy, including a drop in claims for unemployment benefits.
The yield on the 10-year Treasury note rose to 2.09 per cent.