The possible myotoxic effect of bupivacaine in combination with tourniquet ischemia was evaluated in 11 patients who underwent surgery of an arm under intravenous regional anesthesia. Eleven patients with the same kind of surgery and tourniquet who had general anesthesia served as controls. Venous blood bupivacaine concentrations in the anesthetized arm were high at the end of tourniquet time (27.2-202 micrograms/m1) and varied from 2.3 to 12.3 micrograms/ml 10 min after tourniquet release. Changes in blood-gas tensions and plasma potassium and lactate concentrations before and just after tourniquet release correlated with the ischemia time. Changes in creatine phosphokinase, lactate dehydrogenase and aspartate aminotransferase activities, possible indices of loss of integrity of muscle cell membranes, varied considerably and did not correlate with the ischemia time. There were no significant differences between the two groups in any of the parameters. Electron microscopy revealed no evidence of muscle degeneration 24 hr after the use of tourniquet with either bupivacaine intravenous regional (n = 4) or general anesthesia (n = 3).