The purpose of this study was to define the optimum dose of lignocaine required to reduce pain on injection of propofol. We conducted a prospective, randomized, double-blind trial on 310 patients undergoing anaesthesia. Patients were allocated to four groups according to the lignocaine dosage: group A (control), no lignocaine; group B, lignocaine 0.1 mg kg-1; group C, lignocaine 0.2 mg kg-1; group D, lignocaine 0.4 mg kg-1. Our results showed that a dose of lignocaine 0.1 mg kg-1 significantly reduced the incidence of pain and that there was no improvement when the dose was increased.