The non-depolarising muscle relaxants atracurium and vecuronium have been found to exert variable effects on intraocular pressure (IOP). The aim of the present study was to assess the influence of atracurium and vecuronium on IOP under standardized clinical conditions. A total of 40 patients undergoing ophthalmic surgery were randomly allocated to 2 study groups. Following oral premedication with dipotassium clorazepate (0.3 mg/kg), anaesthesia was induced with thiopentone (3-4 mg/kg) and alfentanil (15 micrograms/kg). Muscle relaxation was provided according to randomisation, with patients in group 1 receiving 0.3 mg/kg atracurium and patients in group 2 0.07 mg/kg vecuronium. Anaesthesia was maintained with isoflurane (0.5-0.8 vol%) and 70% nitrous oxide in oxygen. The trachea was intubated 4 min after induction and muscle relaxation. A total of nine measurements of IOP were taken in each patient, starting before premedication and ending 5 min after endotracheal intubation. In both groups, there was a significant decrease in IOP after induction of anaesthesia with thiopentone, alfentanil, and atracurium or vecuronium. No difference in IOP was found between the groups. We conclude that both muscle relaxants can be given when increases in IOP have to be avoided.