The acute hypnotic effects of hydroxyzine 25 mg and 50 mg nocte, were examined in six male and six female volunteers. Continuous electrophysiological measures (C-EEG) were taken to assess both nocturnal sleep and sleep tendency the following day. Both doses produced significant reductions in sleep onset latency and decreases in waking during sleep; reciprocal increases in sleep duration were also seen. Female subjects demonstrated a greater hypnotic response, including a dose-dependent decrease in sleep onset latency. Increases in sleep duration following both doses were significant for the female group alone. C-EEG measures of increased drowsiness the following day failed to achieve significance; although the largest effects on daytime sleepiness, including dose-dependent increases, were again seen with the female subject group and corresponded with subjective ratings. These results demonstrate the hypnotic efficacy of hydroxyzine whilst failing to detect significant C-EEG hangover effects. However, variability in response to antihistamines, registered here as differences between the sexes, requires further consideration.