The cause of a three-alarm fire Friday night at a Center City fraternity house for students at Thomas Jefferson Medical College was under investigation yesterday, said Jim Smith, a spokesman for the Philadelphia Fire Department.

Six firefighters were released from Jefferson after being treated for smoke inhalation and exhaustion, Smith said. No others were injured.

The four-story building at 1025 Spruce St. is owned by Phi Chi Housing Inc., a medical fraternity. Firefighters reported flames shooting through the roof, Smith said.

The first alarm was sounded at 9:04 p.m., the second at 9:49, and the third at 9:54, and the fire was declared under control at 10:50 p.m., Smith said.

- Walter F. Naedele