The residual effects of lormetazepam 1 mg and 2 mg in soft gelatine capsules on driving performance were assessed and compared to those of flurazepam 30 mg, which is also a powerful hypnotic, but possesses a far less favourable pharmacokinetic profile with a long-acting sedative metabolite. Driving performance was tested 10 to 11 h and 16 to 17 h post administration, after 2 days on placebo (baseline), and 2, 4 and 7 days of drug treatment (active), and after 1 and 3 days following the resumption of placebo (washout). The driving test consisted of operating an instrumented motor-vehicle over a 72 km highway circuit in light traffic. Flurazepam 30 mg significantly impaired the ability to control the lateral position of the vehicle compared to placebo baseline measurements. The degree of impairment was substantial in the female subjects and was greater in the morning than in the afternoon. Lormetazepam 1 mg showed no residual effect on driving performance. Lormetazepam 2 mg impaired driving performance to some extent on the following morning, 10 to 11 h post administration, but no residual effect was found in the afternoon. All drugs improved sleep quality and prolonged sleep duration to more or less the same extent.