Forty healthy young volunteers were divided randomly into four equal groups. 2 ml of solutions of pethidine (meperidine) in concentrations of 0.5%, 1% and 1.5% were given to three groups of 10 subjects: a fourth group received saline. Sensory evoked responses obtained via surface electrodes from both sural nerves simultaneously in the pethidine groups and unilaterally in the control group, were evaluated for latency, conduction velocity and amplitude. Sensory changes at the innervation zone were monitored by means of a pinprick. All recordings were obtained prior to injection and at 5 min intervals for 30 min. Concentrations of 1% and 1.5% pethidine were associated with significantly lower amplitudes and with hypoalgesia. Other parameters did not change.