The study was conducted according to a nine-way, observer- and subject-blind, cross-over design. Its purpose was to compare the single-dose effects of the following drugs on driving performance: acrivastine (8, 16 and 24 mg); the combination of acrivastine (8 mg) with pseudoephedrine (60 mg); terfenadine (60, 120 and 180 mg); diphenhydramine-HCl (50 mg); and placebo. The subjects were 18 healthy female volunteers. Drug effects were assessed in two repetitions of two driving tests (highway driving and car-following) after each treatment. Acrivastine's impairing effects in both driving tests were similarly dose-related. The 8-mg dose had a small, but significant, effect on highway driving in the first trial. The 16-mg and 24-mg doses significantly impaired driving in both tests during the first trial and the 24-mg dose did so again during the second trial. Neither the combination of acrivastine with pseudoephedrine nor terfenadine caused any significant impairment of performance. Diphenhydramine significantly impaired driving in both tests during every trial. In conclusion, the normal therapeutic dose of acrivastine (8 mg) had little effect on driving performance, and virtually none when that dose was given in combination with pseudoephedrine (60 mg). Higher doses of acrivastine severely impaired driving performance. Terfenadine had no significant effect on driving performance after any dose while diphenhydramine strongly impaired every important driving parameter.