U.S. stock-index futures signaled a lower open on Wednesday, as Wall Street considered the ADP employment report, which comes ahead of the government's nonfarm payrolls report, out on Friday.
Automatic Data Processing published its January report on private sector employment, with 175,000 jobs created during the month. Economists polled by Reuters had forecast 180,000 jobs were created during the month, down from 238,000 in December.
The ISM non-manufacturing index, which tracks monthly changes in the services sector, will be released at 10:00 a.m. Analysts surveyed by Reuters predict activity crept up to 53.5 in January, from 53.0. Any reading above 50 indicates expansion.
"The tone of U.S. economic data has been on the weak side through most of the year-to-date and hence the markets will be better positioned today for disappointment," said Bank of Tokyo Mitsubishi's Derek Halpenny in a morning research note.
"We maintain that the weakness is temporary and more weather-related than anything. The prospects for stronger more sustainable growth remain good."
(Read more: Wicked winter weather chills U.S. economy, stocks)
Companies reporting quarterly results before Wall Street opens included Dow component Merck, which posted quarterly sales slightly below expectations, hurt by competition from cheaper generic drugs. It forecast full-year earnings at the low end of Wall Street estimates.Its shares were up nearly 3 percent in early New York trading.
Federal Reserve speakers on Wednesday include Charles Plosser, a hawkish, voting member of the FOMC (Federal Open Market Committee), and Dennis Lockhart. Also, Fed Governor Daniel Tarullo will testify on the Volker Rule before the House Financial Services Committee.
The uptick in the U.S. helped boost European and Asian shares early on Wednesday.
(Track: European shares with CNBC)
—By CNBC's Katy Barnato