Caterpillar led the Dow Jones industrial average lower after missing analysts' estimates for earnings and revenue.
The S&P 500 was down six points, or 0.4 percent, to 1,748 after the first few minutes of trading Wednesday.
The Dow was down 46 points, or 0.3 percent, to 15,420. The Nasdaq composite was down 21 points at 3,908.
Caterpillar's quarterly earnings plunged 44 percent and the company cut its outlook for the year again. Caterpillar dropped $5, or 5.6 percent, to $84.17.
Boeing rose $5.26, or 4 percent, to $127.74 after its earnings beat Wall Street's forecasts.
Markets also fell in Europe and Asia.
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