Trading on the floor of the Nasdaq stock market's Philadelphia Stock Exchange was halted for an hour because of smoke.
The exchange, known as Nasdaq OMX PHLX, handles options trading.
Nasdaq OMX Group said its employees were evacuated.
The Philadelphia Fire Department was trying to determine the origin of the smoke.
Trading was halted at 11:05 a.m. Tuesday and all smoke had been cleared from the floor by 12:05 p.m., and trading resumed about 35 minutes later, NASDAQ OMX said in a statement.
Nasdaq acquired the Philadelphia Stock Exchange, the nation's oldest stock exchange, in July 2008.