Flight 503, bound for Burbank, had taken off but was still nearby when Oakland firefighters got a call about 7:20 a.m. reporting a medical emergency at the airport, a fire spokesman said.
The plane touched back down safely, and an airport dispatcher said the fumes had dissipated when safety crews boarded. It was not immediately clear what had caused the fumes.
The flight attendant was taken to a hospital for observation, the dispatcher added.
It does not appear that anyone else suffered symptoms, an airport official said.
Southwest Airlines spokesman Brad Hawkins said there were 137 passengers on the plane, plus a crew of five. He said the passengers are being put onto another flight and will probably arrive in Burbank about two hours later than scheduled.
Bay City News Service contributed to this report. Full story, here.