Edgy officials evacuated 16 subway stations, shut down Red Line traffic and closed Wilshire Boulevard during the evening rush hour Wednesday after some subway passengers complained of itchy eyes and dizziness.
More than 25 people, including two police officers, were treated by paramedics. The two officers and an elderly woman were taken to a hospital, but no one appeared to be seriously injured.
The cause of their symptoms was not determined, but officials said it could have been anything from a minor gas leak to high pollen counts and the current spate of dry, hot weather.
Fears by terrorist-conscious officials that it might be something much worse prompted a strong response to initial reports at 5:10 p.m. that something had overwhelmed two Los Angeles police officers patrolling the Red Line station at MacArthur Park.
The officers called for help. Several dozen police units and 20 fire engines responded, along with eight ambulances.
"Given the national situation, they erred on the side of caution," said Bill Heard, a spokesman for the Metropolitan Transportation Authority.
"This is an emergency!" speakers blared in Red Line stations from North Hollywood to Union Station. "Exit the station immediately."
Trains stopped at the nearest station, and passengers streamed up to the surface.
Paramedics treated 27 people at the Wilshire/Western station for minor eye irritation. After examination at the scene, the two police officers and an elderly woman were taken to the Cedars-Sinai Medical Center, where they were treated for nausea and shortness of breath before being released.
Los Angeles Fire Capt. Richard Andrade said department chemists tested the subway station for everything from poison gases to neurological toxins and tear gas.
"We didn't find anything," Andrade said.
As a precaution, Wilshire Boulevard was shut down for several blocks on either side of the MacArthur Park station, snarling traffic in the area for several hours.
Wetenayet Girma said the 357-line bus she takes down Wilshire to classes at Santa Monica City College was detoured onto a side street.
"We would move like an inch, and then it would stop again," she said.
Oscar Hildalgo, who runs a small novelty stand near the Wilshire/Western station, said the stalled subway passengers seemed to take it all in stride, with no signs of anxiety.
"They were just asking what was going on," he said. "It didn't seem like much to me."
The MTA sent extra buses to all the Red Line stations so passengers could complete their journeys.
At 7 p.m., after a thorough search, the MTA reopened the Red Line stations and subway traffic resumed. Wilshire Boulevard was reopened to vehicular traffic about the same time.