Nasdaq did not publish quotes for its main indexes after the market opened on Friday due to a data outage, but individual stock quotes were unaffected.
Nasdaq Omx Group Inc said it was investigating a problem with its global index data service that affected index quotes dissemination.
Traders said there were no quotes for the Nasdaq composite and the Nasdaq 100 index. Individual share price quotes did not appear to be affected.
"There seems to be a data feed issue. It is making people hesitant to make decisions. A lot of traders base this index as sort of a sign post for trading. It's like someone just turned off the light," said Kevin Kruszenski, head of listed trading at KeyBanc Capital Markets in Cleveland.
The Nasdaq said in an emailed alert it would further advise on the situation. A Nasdaq spokesman had no comment.