The study was conducted to evaluate neuropsychological symptoms, subjective stress and response speed functions in subjects occupationally exposed to low levels of anesthetic gases. A group of 112 operating theatre personnel exposed to anesthetic gases (nitrous oxide and isoflurane), and 135 non exposed hospital workers from 10 hospitals in Northern Italy were examined before and after the shift on the first and the last day of the working week. Three different tasks were administered: a complex reaction time test (the Stroop Color Word); a questionnaire for neuropsychological symptoms (EURO-QUEST); the block design subtest (WAIS). Biological and atmospheric indicators of exposure were measured. In the exposed group, the geometric mean of urinary nitrous oxide at the end of the shift was 7.1 micrograms/l (95th percentile 12.4, range 1.5-43) on the first and 7.8 micrograms/l (95th percentile 21.5, range 1.0-73.3) on the last day of the working week. On the same days, end of shift urinary isoflurane was 0.7 microgram/l (95th percentile 2.6, range 0-4.7) on the first day and 0.8 microgram/l (95th percentile 2.0, range 0-5.6) on the last. The exposed and control subjects were comparable for both basic intellectual abilities and subjective stress levels. No statistical differences were observed between exposed and control subjects for neuropsychological tests and symptoms. No dose-effect relationships were observed between the exposure indicators and the test results. In conclusion, no early behavioral effect on the central nervous system was detectable at the exposure levels measured. The biological exposure limits of 13 micrograms/l for nitrous oxide and 1.8 micrograms/l for isoflurane corresponding respectively to the atmospheric concentrations of 25 ppm and 0.5 ppm seem to be adequately protective for the integrity of workers' neurobehavioral functions, as measured with the tests used.