Stocks fell at the open on Monday as a lack of confidence in steps to shore up ailing banks persisted, offsetting Merck's proposed takeover of Schering-Plough .

The Dow Jones industrial average <.DJI> dropped 45.08 points, or 0.68 percent, to 6,581.86. The Standard & Poor's 500 Index <.SPX> fell 4.85 points, or 0.71 percent, to 678.53. The Nasdaq Composite Index <.IXIC> lost 5.92 points, or 0.46 percent, to 1,287.93.

(Reporting by Rodrigo Campos)