Some analysts were looking forward to Thursday's gross domestic product figure and first-time jobless claims, hoping to find reasons to remain bullish about the economy. A report on payroll growth, due April 2, could be pivotal in shoring up shares — or causing another drop-off.

"If we get any evidence job growth is picking up, that'll make people a lot better," said Chip Dickson, equities analyst with Lehman Brothers. "Until then, I don't expect a lot of conviction in this market either way."

Individual companies have attracted interest, however. Apple Computer Inc. was upgraded from "neutral" to "buy" by FTN Midwest, citing strong computer and digital music player sales. Apple ended the session unchanged at $25.86.

Wal-Mart Stores reported March sales would come in at the high range of forecasts, but its shares fell 50 cents to $58.10.

Cancer-care services provider U.S. Oncology Inc. jumped $2.44, or 19 percent, to $15.14 after it said it will be acquired by private equity firm Welsh Carson Anderson & Stowe for $1.7 billion. The deal was expected to be completed by the second quarter.