Fairfax County's Oakton High School was evacuated yesterday and 22 students and a teacher were taken to hospitals for observation and treatment after they were exposed to fumes of an unidentified chemical in a science lab.

All of the students taken to hospitals were released by evening. The teacher, whose name wasn't released, remained at Inova Fairfax Hospital in fair condition.

The leak was discovered just after 10 a.m., and officials later closed the school for the rest of the day as a hazardous-materials team arrived. Fire officials said a leaking container of the chemical was packaged and sent to a lab for analysis and identification.

Fire officials cleared the building for reopening late yesterday.

School officials said the leak apparently originated in a cupboard where chemicals had been stored. A teacher found several unlabeled containers of chemicals in the cupboard Thursday. Under district policy, the chemicals were supposed to be labeled. The teacher removed the containers and placed them under a special ventilation hood for safety to await removal by a district risk-management specialist.

Yesterday, however, a colleague from a neighboring classroom went into the lab and told the teacher that there was an unusual smell coming from the room. The smell was traced to the cabinet where the chemicals had been stored. When the teacher opened the cupboard, she was overcome by the fumes, officials said.

Fire officials said the teacher and students complained of dizziness, nausea and shortness of breath.

The teacher and 12 students are taken to Inova Fairfax Hospital. Six students were taken to Reston Hospital Center, and four were taken to Inova Fair Oaks Hospital.

Students and staff were evacuated to the school's football stadium. Later, buses were sent to pick up students and take them home.

School officials said the building will be open from 8 to 11 a.m. today so students can pick up belongings. Students should report to the office to be escorted to classrooms. On Monday, students are to report to their fourth-period classes first to retrieve items not already picked up.

School officials said they're still investigating. Parents seeking more information can call a hot line at 703-319-2700.