The S&P 500 was down almost 6 percent for the year at the start of February amid concerns about slowing growth in China and other emerging markets, as well as worries about the state of the U.S. economy. Since then stocks have rebounded, but some investors aren't convinced the recovery will last.
"I've felt all along that this is going to be a very volatile year," said Uri Landesman, president of Platinum Partners, an investment management company. "For me, you've got a lot more downside than upside."
The S&P 500 rose almost 30 percent last year, and investors are now too bullish on the stock market, making it vulnerable to a sell-off, Landesman said.
Ameren, a utility company based in St. Louis, Mo., was among the winners on Friday.
The stock rose $2.07, or 5.3 percent, to $40.88, making it the biggest gainer in the S&P 500. Ameren reported earnings that beat Wall Street's expectations after cold weather boosted demand for gas and electricity.
Among other stocks making big moves on Friday:
— Intuit rose $3.39, or 4.6 percent, to $77.24 after the maker of Quicken, TurboTax and other financial software raised its earnings forecast for its fiscal third quarter. Intuit said it was off to a good start in tax season and that electronic tax filings using TurboTax were up 10 percent as of Feb. 14.
— Priceline.com climbed $32.65, or 2.5 percent, to $1,315.65 after the online travel company reported earnings that exceeded the expectations of Wall Street analysts, as bookings for hotels, rental cars and airline tickets accelerated.