Administration of 22 μg/kg pancuronium to 11 conscious subjects decreased grip strength to 23.6± 5.4 per cent of control within 5 minutes. Grip strength returned to 86.0± 4.7 per cent of control in 25 minutes and vital capacity to 97.0±2.0 per cent of control in 15 minutes. Exercising at a fast rate during partial block caused rapid fatigue. Administration of edrophonium or neostigmine at the height of the block caused rapid but incomplete return of grip strength. In 11 lightly anesthetized subjects 40 μg/kg pancuronium decreased the twitch tension of the indirectly stimulated adductor pollicis muscle to 11.5 ±2.8 per cent and tidal volume to 71.4± 7.4 per cent of control by 5 minutes. Tidal volume recovered by 15 minutes, but twitch tension was only 66.9 ± 6.0 per cent of control at 60 minutes. The administration of edrophonium or neostigmine at this time had little or no effect on twitch tension. Tetanic stimulation applied 10 to 15 minutes later showed well-maintained tetanus, which was followed by significant posttetanic facilitation and maintenance of the twitch tension above the pre-drug control level for the remainder of the 10- to 15-minute observation period. Moderate elevation of pulse rate was the only significant circulatory change.