Psychological effects of halothane (16 subjects) and isoflurane (24 subjects) anesthesia on healthy young men were assessed prior to and 2,3,4,6,8, and 30 days after anesthesia. The results with each agent were compared with each other and with the results for 41 unanesthetized controls. Both agents altered psychological function. Changes in function were greatest 2 days after anesthesia; function had returned to near preanesthesia values 8 days after anesthesia. Only slight symptom and mood effects and no intellectual effect attributable to anesthesia remained 30 days after anesthesia. Halothane produced greater negative effects on moodds and symptoms and tended to produce greater negative effects on intellectural function than did isoflurane. The differences between the two anesthetics are consistent with differences in their solubilities and metabolism.