Objective studies about the duration of action pancuronium (PCM) in renal failure patients are scarce. This study was undertaken to obtain more complete information on spontaneous reversal from PCM-induced neuromuscular block by monitoring the twitch height to full recovery in the absence of any potentiating agent. Thumb abduction was monitored by a deplacement transducer in end-stage renal failure (ESRF) and in control patients without renal failure (RF) during neuroleptanalgesia after 0.04 mg/kg and 0.08 mg/kg PCM administration. In the small dosage series, the prologation of action in ESRF becomes significant for the 75% recovery level (mean values +/- s.e.mean:control: 42 +/- 7 min, ESRF: 71 +/- 10 min, P less than or equal to 0.05). In the second series (0.08 mg/kg), the 50% recovery level is already significantly delayed in ESRF patients (control: 91 +/- 7 min, ESRF: 163 +/- 27 min, P less than or equal to 0.05). The 100% twitch height recovery is obtained with 0.04 mg/kg PCM within 65+/- 7 min for patients without RF and within 103 +/- 9 min in ESRF patients (P less than or equal to 0.01). For the 0.08 mg/kg PCM dose, these figures are, respectively, 139 +/- 9 min and 214 +/- 20 min (P less than or equal to 0.01). The prolongation of PCM action in ESRF is in agreement with the pharmaco-kinetics of the drug. Large dosages of PCM must be avoided in ESRF patients because it delays spontaneous full recovery for too long.