The central nervous and cardiovascular effects of midazolam 0.15 mg kg-1 were studied in 20 healthy, unpremedicated volunteers (10 male and 10 female). No important side-effects were noted and the venous tolerance to midazolam was excellent. Three minutes after injection mean systolic arterial pressure decreased from 121 +/- (SEM) 2 mm Hg to 115 +/- (SEM) 2 mm Hg and diastolic pressure from 78 +/- 2 to 70 +/0 2 mm Hg (P < 0.05), and these effects persisted for at least 20 min. Heart rate increased from 77 +/- 4 beat min-1 to 90 +/- 3 and 88 +/- 3 beat min-1 and 3 min after the injection (P < 0.05). Anterograde amnesia (40 +/- 3 min duration) and drowsiness (lasting 128 +/- 23 min) were observed in all subjects. Loss of the eyelash reflex and apnoea were observed more often in the male group than in the female subjects. Midazolam 0.15 mg kg-1 was not sufficient to induce anaesthesia reliably in healthy unpremedicated volunteers.