Nitrous oxide and halothane, in respective concentrations as low as 50 parts per million (ppm) and 1.0 ppm, caused measurable decrements in performanceon some psychological tests taken by healthy male graduate students. Nitrous oxidealone caused similar concentrations of anesthetics were visual perception, immediate responses required in a task of divided attention to simultaneous visual and auditory stimuli. These effects were absent in subjects exposed to 25 ppm N20 and o.5ppm halothane. Findings from this study suggest that N20 and haloghane levels in the ambient air of hospital operating rooms should not exceed 25 pp. N20 and 0.5ppm halothane.