A multicentre, parallel group hospital study was carried out in 190 subjects with insomnia to compare the efficacy, incidence of hangover and the side-effects of loprazolam and nitrazepam. Following 2 nights single-blind phase on placebo, loprazolam (1.0 mg), nitrazepam (5.0 mg) or placebo was administered double-blind for 7 consecutive nights. Visual analogue scales and questions were used to rate efficacy. There was no statistically significant difference between loprazolam and nitrazepam for 'ease of getting to sleep', 'restfulness of sleep' and 'depth of sleep'. Like nitrazepam, loprazolam diminished the number of periods of wakefulness and made it 'easier to get to sleep again'. Subjective evaluation showed that hangover was not a feature of loprazolam. It did not affect morning alertness and patients thought they had improved balance and co-ordination while on this drug. These findings are in keeping with the evidence of other workers who have shown only minimal psychomotor impairment, if any, with loprazolam (1.0 mg). There was no statistically significant difference between treatments with respect to frequency or incidence of side-effects.