U.S. stocks turned lower on Friday in volatile trading as banks fell on concern over what the government's stress tests will show after the release of the results was delayed.

Shares of JPMorgan Chase & Co fell 1.6 percent to $32.47, making it a top drag on the KBW bank index <.BKX>, which was down 1 percent.

The results from stress tests of the 19 largest U.S. banks are expected to be released on May 7, a government source said Friday, and are expected to show how much capital the weakest firms will need to raise should the economy weaken further.

There's some apprehension about the stress tests next week and the fact that (the results) were pushed back I think is more of a negative sign, said Michael James, a senior trader at Wedbush Morgan in Los Angeles.

Economic reports showed the U.S. factory sector shrank further in April but at a slower pace and consumers felt more confident about the economy last month than at any time since September.

Energy shares helped stocks to make gains in the afternoon. Exxon Mobil Corp was up 1.3 percent at $67.55, and the S&P energy index gained more than 2 percent after crude oil futures rose 3 percent to $52.90 a barrel.

The energy stocks, if you can determine the word cheap, are reasonably priced, said Carl Birkelbach, chairman and CEO of Birkelbach Investment Securities in Chicago.

If the economy is going to turn, which is what the market, the Fed and Obama are telling us, then naturally energy prices should go back up again.

The Dow Jones industrial average <.DJI> dropped 19.59 points, or 0.24 percent, to 8,148.53. The Standard & Poor's 500 Index <.SPX> dropped 1.00 point, or 0.11 percent, to 871.81. The Nasdaq Composite Index <.IXIC> dropped 4.64 points, or 0.27 percent, to 1,712.66.

Investors decided to book some gains after a solid April, which limited the advance. McDonald's was the top drag on the Dow after Goldman Sachs removed the fast-food chain from its conviction buy list, although it affirmed its positive rating.

Shares fell 1.5 percent to $52.49.

April marked the S&P 500's best month in nine years in terms of percentage gains, with a 9.4 percent climb.

MasterCard Inc , the world's second-largest credit card network, was also among the laggards after it said revenues will grow less than expected in 2009.

MasterCard shares were down 7.3 percent at $170.01.

On Nasdaq, the index was led higher by major technology companies such as Apple , up 1.3 percent to $127.42 and Research In Motion , up 4.8 percent to $72.86.

Shares of Celgene were the biggest drag on the index after it reported first-quarter results that were in line with the company's forecast, but the cancer drugmaker said that it expects its full-year earnings to come in at the low end of its previously announced range.

The Amex Biotechnology Index <.BTK> slipped 1.3 percent.

(Reporting by Chuck Mikolajczak; Editing by Kenneth Barry)