The influence of diazepam on some adverse effects of succinylcholine was studied double-blind. Thirty patients (ASA I-II) were allocated to groups receiving either diazepam 0.08 mg/kg or d-tubocurarine 0.05 mg/kg 5 min before a bolus of succinylcholine, 1 mg/kg and 1.5 mg/kg, respectively. Fasciculations were more frequent in the diazepam group (80%) than in the d-tubocurarine group (13%). Relaxation, onset and duration of neuromuscular blockade were comparable in the two groups. The rise in intraocular pressure after succinylcholine and endotracheal intubation was small (0.27 kPa = 2 mmHg) but significant (P less than 0.01) after diazepam pretreatment. In this group the rise in intraocular pressure was 50% lower than the rise seen in the d-tubocurarine group (P less than 0.01). We conclude that pretreatment with diazepam 0.08 mg/kg will reduce but not prevent a rise in the intraocular pressure after succinylcholine in a rapid sequence induction. In the management of patients with penetrating eye injuries the use of succinylcholine still carries some risk even after diazepam pretreatment.