The new H1-antagonist acrivastine (BW825C) in doses of 4, 8, and 16 mg was compared with triprolidine HCl (2.5 and 5 mg) in a double-blind crossover study in 12 subjects. Adaptive tracking performance 1.5 hours after dosing was impaired by triprolidine, 2.5 and 5 mg; the impairment was still detectable 3.5 hours after 5 mg. Acrivastine did not impair adaptive tracking after any of the doses. Triprolidine increased reaction times after 1.5 hours (2.5 and 5 mg) and 3 hours (5 mg), but acrivastine did not have any effect on reaction time at any dose. Both doses of triprolidine caused subjective central nervous system effects after 1.5 hours, and triprolidine, 5 mg, still had some detectable effects on subjective rating scales after 3 hours. No subjective effects were noted after acrivastine. We conclude that acrivastine at doses causing more peripheral H1-antagonism than triprolidine has considerably reduced central nervous system activity.