Stocks fell at the open on Monday after four weeks of gains, as a spike in the U.S. dollar weighed on commodity prices and dried up bids on other risky assets.

The Dow Jones industrial average <.DJI> fell 99.15 points, or 0.81 percent, at 12,131.96. The Standard & Poor's 500 Index <.SPX><.INX> lost 12.79 points, or 1.00 percent, at 1,272.30. The Nasdaq Composite Index <.IXIC> dropped 30.10 points, or 1.10 percent, at 2,707.05.

(Reporting by Chuck Mikolajczak; editing by Jeffrey Benkoe)