BACKGROUND: Cyclosporine, an immune suppressive agent has been reported to potentiate the neuromuscular blockade induced by vecuronium and atracurium. And the potentiation degree was more prominent in the vecuronium. Rocuronium and mivacurium have been introduced into clinical practice recently and there is no report whether the cyclosporine potentiates the neuromuscular blocking effects of these agents. We, therefore studied the effect of Sandimun (cyclosporine in cremophor-ethanol) on the neuromuscular blockade action of rocuronium and mivacurium in rabbits. METHOD: The effect of Sandimun on the rocuronium and mivacurium were investigated in anesthetized 30 rabbits. The rabbits were divided into five groups; rocuronium group (rocuronium bromide 1 mg/kg iv), rocuronium - Sandimun group (rocuronium bromide 0.1 mg/kg iv after Sandimun 5 mg/kg iv), mivacurium group (mivacurium chloride 0.064 mg/kg iv), mivacurium - Sandimun group (mivacurium chloride 0.064 mg/kg iv after Sandimun 5 mg/kg iv) and Sandimun group (Sandimun 5 mg/kg iv). Neuromuscular block was assessed by measuring the response of anterior tibial muscle to 0.1Hz single twitch stimulation of the common peroneal nerve. Onset time, duration of muscle relaxation and recovery index were compared among the groups. RESULTS: There were no significant differences in onset time and recovery indices among the groups. Significant difference was found in duration between the rocuronium group and the rocuronium-Sandimun group (p<0.05). CONCLUSION: Sandimun potentiates the rocuronium - induced neuromuscular blockade but not the neuromuscular blocking action of mivacurium.