U.S. stocks opened little changed on Friday but strong quarterly results from Caterpillar and Merck looked set to drive the Dow to its best month since December.

The Dow Jones industrial average <.DJI> was up 15.67 points, or 0.12 percent, at 12,778.98. The Standard & Poor's 500 Index <.SPX> was up 0.12 points, or 0.01 percent, at 1,360.60. The Nasdaq Composite Index <.IXIC> was down 2.61 points, or 0.09 percent, at 2,869.92.

(Reporting by Ryan Vlastelica)