A double-blind, daytime, placebo-controlled study was carried out in 12 healthy volunteers to investigate the effects of single doses of 5, 15 and 30 mg temazepam and of 5 and 10 mg nitrazepam on the EEG, psychomotor performance, subjective mental and emotional status, blood pressure and heart rate. Each subject received all 6 treatments in a random sequence at intervals of 1 week. The EEG tracings were evaluated quantitatively by spectral analysis. Psychomotor performance was assessed by means of the tapping test. Subjective mental and emotional status were assessed using the Bond and Lader analogue self-rating scale. Procedures were carried out before and at 1/2, 1, 2, 4, 6, 7, 8 and 9 h after drug administration, with the exception of the tapping test, which was carried out before and, again, after 2 and 7 h. EEG estimates of equipotency, based on magnitude of peak effect, were as follows: 15 mg temazepam approximately 5 mg nitrazepam; and 30 mg temazepam greater than or equal to 10 mg nitrazepam. At these approximately equipotent doses, temazepam had a somewhat earlier onset of action on the EEG, a clearly shorter duration of EEG action, and lesser impairment of psychomotor performance than nitrazepam. Qualitatively, both drugs had similar effects on the subjective mental and emotional states of the subjects. There were no clinically relevant changes in mean or individual sitting and standing blood pressure values. After temazepam, but not after nitrazepam, heart rate increased (maximal mean change 10 bpm) as part of a normal startle response to arousal. The results suggest that temazepam has less hangover potential than nitrazepam.