U.S. stocks rose on Wednesday as investors scooped up bargains in the commodities sectors a day after Wall Street slid to a 10-week low, but sentiment was dampened by the start of the quarterly earnings season.

Amgen Inc shares shot up 16 percent to $60.59, one day after the biotechnology company reported positive results for its experimental osteoporosis drug. The S&P healthcare index <.GSPA> rose 1.2 percent.

Investors were reticent to buy aggressively after Tuesday's selloff as uncertainty over second-quarter earnings loomed. Alcoa Inc , the first Dow component to report, is expected to post its third consecutive quarterly loss after markets close on falling demand for aluminum. Alcoa rose 2.1 percent to $9.61.

After a rally that took the S&P 500 index up 40 percent from 12-year lows in early March, traders are looking for hard evidence that the economy will rebound from a deep recession.

David Sowerby, market strategist for Loomis Sayles in Detroit, said the 2 percent drop in the S&P 500 was prompting tepid buying, but cited anxiousness over earnings.

Given that the more important economic numbers have been soft the last two weeks, it's been somewhat of a cold shower for earnings expectations, he said.

The Dow Jones industrial average <.DJI> rose 36.42 points, or 0.45 percent, to 8,200.02. The Standard & Poor's 500 Index <.SPX> added 3.64 points, or 0.41 percent, to 884.67. The Nasdaq Composite Index <.IXIC> gained 5.31 points, or 0.30 percent, to 1,751.48.

Raw materials <.GSPM> was the leading sector in the S&P 500, up nearly 1 percent after a 2.5 percent slide on Tuesday.

Microsoft Corp was the biggest drag on the Dow industrials. Google Inc said it will launch a new operating system in the second half of 2010, taking on Microsoft's core business.

Microsoft shares fell 1 percent to $22.30, while Google rose 1.6 percent to $403.09.

Leaders of the Group of Eight richest nations and the major developing powers gathered for a three-day summit in Italy. They are expected to agree the world's economy is still too weak to remove stimulus measures.

(Reporting by Rodrigo Campos; additional reporting by Leah Schnurr; editing by Jeffrey Benkoe)