We have studied the effects of temazepam, alone and in combination with ethanol, on psychomotor performance in six healthy men and women using a battery of five microcomputer-based tasks before and 30, 90, and 150 min after treatment. The tests were pursuit tracking, divided attention, two four-choice reaction time tests and tapping rate. The entire battery required 25 min. The subjects also reported their mood at each testing time using a computerized bipolar mood scales test. Temazepam (15 mg) plus ethanol (peak blood concentration of 11 mmol.l-1) significantly impaired divided attention, tracking, and reaction time over a 3 h period. There was significant impairment versus placebo for each drug alone on some of the tests. Plasma and urine concentrations of temazepam and temazepam glucuronide were measured, but there was no significant temporal correlation between impairment and drug or metabolite concentration in either plasma or urine. The subjects knew when they had taken ethanol, but could not discriminate temazepam from ethanol whether alone or in combination. The subjects rated their performance similarly after each of the four treatment conditions. The performance on the tracking, divided attention, and PAB reaction time tasks used in this study was impaired by a combination of temazepam and ethanol in doses which may not cause impairment when each is given alone.