Dosc-response relationships for a 1:4 weight ratio-mixture of pancuronium and metocurine were studied during inhalational anesthesia with halothane and isoflurane in patients with and without renal failure. The time for recovery from 10 to 20% of control thumb twitch tension also was determined. In subjects with normal renal function, relaxant doses required for 95% twitch height suppression (ED95) were 50% of those predicted by simple addition of effects when used with a balanced anesthetic technique, 37% of predicted when used with 1.3 MAC halothane, and 25% of predicted when used with 1.3 MAC isoflurane (P< 0.05). In subjects with renal failure, ED95values for the combination were 40% of predicted when used with 1.2 MAC halothane and 45% of predicted when used with 1.2 MAC isoflurane (NS). For relaxants used singly in renal failure, pancuronium alone was slightly enhanced by 1.2 MAC halothane (85% of predicted), while 1.1 MAC isoflurane reduced the ED95to 57% of predicted (P< 0.05). Similar results were obtained for metocurine alone when used in renal failure (77 and 58% of predicted when used with halothane and isoflurane, respectively) (NS). Predicted values are published results for balanced anesthesia in normals. Recovery times were prolonged twofold in renal failure (P< 0.05). Thus, the combination of pancuronium and metocurine is synergistic to the same degree in normals and in renal failure patients, but the total blockade produced by the combination is enhanced by halothane and isoflurane only in normals.