(REUTERS) -- Stocks were lower on Wednesday after the S&P 500 notched its biggest gain in a month, weighed down by IBM and Intel after their quarterly results.

The benchmark S&P on Tuesday climbed 1.55 percent, its biggest percentage gain since March 13, as Coca-Cola Co led a round of solid earnings reports and on easing concerns over the euro zone debt crisis.

Investors don't like volatility but large run-ups can be equally unsettling too because investors question if that is going to hold, said Tim Speiss, a partner at Eisner Amper in New York.

According to Thomson Reuters data, 22 companies in the S&P 500 were expected to report on Wednesday, including American Express Co , Qualcomm Inc and eBay Inc after the close.

Of the 56 S&P 500 companies reporting through Wednesday morning, 79 percent beat Wall Street estimates.

International Business Machines Corp and Intel were the biggest drags on the Dow after the technology bellwethers posted quarterly results late Tuesday. IBM lost 2.4 percent to $202.56 and Intel fell 2 percent to $27.88. The PHLX semiconductor index <.SOX> declined 1.5 percent.

Investors should not overreact to positive news nor should they be overreacting to really what could be viewed as isolated earnings reports. One report does not make a trend, unfortunately, said Speiss.

The Dow Jones industrial average <.DJI> dropped 56.99 points, or 0.43 percent, to 13,058.55. The Standard & Poor's 500 Index <.SPX> lost 4.68 points, or 0.34 percent, to 1,386.10. The Nasdaq Composite Index <.IXIC> fell 6.36 points, or 0.21 percent, to 3,036.46.

Yahoo Inc gained 3.3 percent to $15.51 after posting an uptick in revenue, its first quarterly sales growth in three years, as new the chief executive outlined his plans to revamp the struggling Internet media company.

Halliburton Co advanced 4.1 percent to $34 after the world's No. 2 oilfield services company said North American revenue reached a record high. The PHLX oil service sector <.OSX> gained 1.1 percent.

SXC Health Solutions Corp will buy pharmacy benefit manager Catalyst Health Solutions Inc for about $4.4 billion. Catalyst jumped 30 percent to $82.64 and U.S.-listed shares of SXC Health climbed 6.5 percent to $85.50.

Genworth Financial Inc slid 18 percent to $6.32 and was the worst performer on the S&P 500 after the life and mortgage insurer pushed back the initial public offering of an Australian unit.

Berkshire Hathaway Inc Chief Executive Warren Buffett said he has stage 1 prostate cancer that is not remotely life-threatening or even debilitating in any meaningful way. Berkshire Class B shares lost 1 percent to $80.03.

(Reporting By Chuck Mikolajczak; editing by Jeffrey Benkoe)