The effect of oxatomide, an antiallergic drug, on the central and peripheral nervous systems were investigated, and the following results were obtained: Oxatomide at oral doses of 30-100 mg/kg produced little or no effect on the spontaneous and cooperative movements in mice, hexobarbital-induced hypnosis in mice, body temperature in rats, and did not induce muscle relaxation, the analgesic effect, anticonvulsive effects and anti-physostigmine effect. Oxatomide at doses of 300 mg/kg or more produced sedation followed by an increase in the responses to stimuli in mice and rats. These behavioral changes diminished within 7-8 hours. Oxatomide (2 mg/kg, i.v.) changed the EEG to a slightly drowsy pattern in unanesthetized, unrestrained rabbits. Neither the EEG arousal responses evoked by auditory stimulation or electrical stimulation to the mesencephalic reticular formation, nor the limic afterdischarges induced by electrical stimulation to the hippocampus or amygdala were affected by oxatomide at any of the doses employed. Oxatomide had no effect on the spinal reflex in cats, conditioned behavior in rats or local anesthesia in guinea pigs. These results suggest that oxatomide shows little effect on the central and peripheral nervous systems at a dose sufficient to elicit the antiallergic actions.