Synergism occurs between some combinations of non-depolarising muscle relaxants. To test the effect of pancuronium as a priming dose of atracurium, 45 adults were anaesthetised with 25 micrograms/kg alfentanil. 75 micrograms/kg midazolam, and 0.25 mg/kg edomidate, O2/N2O and enflurane, and were randomised to one of three groups. After induction, 15 patients received 0.5 mg/kg atracurium, 15 were primed with 0.075 mg/kg atracurium and another 15 with 0.0125 mg/kg pancuronium and three minutes later 0.45 mg/kg atracurium. Neuromuscular response was monitored by adductor pollicis electromyogram (EMG) by stimulating in a TOF pattern. Times for tI reduction of 75, 50, 25 and 0% and tI recovery to 10% were taken. There were no differences between the two groups that received only atracurium. The pancuronium priming group showed a significantly faster onset of neuromuscular blockade (tI = 0%: control group I: 76.3 +/- 15.4 sec vs. pancuronium group III: 64.3 +/- 11.3 sec) and a prolonged recovery. Pancuronium priming can shorten the onset time of atracurium while atracurium priming alone showed no shortening. This suggests a synergism for pancuronium priming in combination with atracurium.