Studies were carried out in normal healthy male subjects to assess the effects on psychomotor functions and subjective ratings of performance after acute administration of azatadine maleate, a potent antihistamine with additional antiserotonin activity. In the first trial, 2 mg azatadine was compared with another new antihistamine Sch 12169 (2 mg) and placebo. In a second trial, higher doses of azatadine (4 mg and 8 mg) were compared with dexchlorpheniramine (4 mg) and placebo. Both trials were of a double-blind, randomized Latin square design and subjects were assessed using a battery of tests, after administration of each trial drug. The time and sequence of tests were standarized, with a 1-week interval between test sessions. The results showed that azatadine did not produce significant impairment of psychomotor function at either the standard 2 mg or the maximum recommended 4 mg per day dosage level. Permormance was only significantly impaired, compared with that after placebo, at the 8 mg dose level and was of a similar order to that observed after dexchlorpheniramine at the usual 4 mg dosage. It is suggested, therefore, that at the normal recommended dosage of 2 mg per day, azatadine is not likely to impair driving ability.