A fire alarm rang through the Science Center late yesterday morning, interrupting exams in two lecture halls and forcing the evacuation of hundreds of students and professors.

The alarm, which was pulled on the Science Center's second floor at 11:50 a.m., sounded as students in Statistics 100 and Chemistry 17 struggled to complete exams. Cambridge fire department officials found no evidence of a blaze.

George M. Carbone, fire and safety supervisor on facilities maintenance, called the alarm an "unfortunate prank." He was not able to identify the perpetrator.

Students taking the statistics test initially stayed in their seats, according to Assistant Professor of Statistics Alan Zaslavsky.

But when the alarm didn't stop, Zaslavsky dismissed the class a few minutes early. As a result, the professor announced yesterday afternoon that he will allow his students to retake the exam.

Students said they were upset about the alarm.

"The test was really the type that you had to concentrate really hard on," said Terrell P. McSweeney '97. "And not only was the dissonant bell bad enough, what was worse was that people kept on interrupting our exam, telling us people were evacuating the building. We stayed because no one got up, and also because there was only five minutes left in the class."

McSweeney called the decision to offer a re-test fair but "somewhat of an inconvenience."

Alisa N. Kendrick '97 also said she found the alarm distracting.

"It was a really hard test and the bell just became a distraction," she said. "What was even worse was that one of the proctors ran up to the back and held the bell in his hands to try and muffle the sound....Professor Zaslavsky came in to the room and dismissed us all, saying he would take the alarm 'into account.'"

In an e-mail message to the course's students, Zaslavsky denounced the false alarm and apologized for the disruption.

"I regret the disruption that was experienced by students taking the exam in Science Center C, but unfortunately we cannot entirely insulate ourselves from the acts of malicious or thoughtless people," he wrote.

Chemistry 17 was evacuated, but only "after we found it was a fire alarm," said graduate student Alan Annis, the course's head teaching fellow. "We couldn't tell at first what the ringing in the hallway was. We thought it was someone ringing some dinky bell."

A member of the lecture hall technical staff informed Annis of the alarm.

"The bell was ringing but no one moved. Several people even came in to tell us about the alarm," said chemistry student Victor Chiappa '98. "I can definitely see how the alarm could have affected people's performance on the test."