Acute renal failure was induced to investigate it effects on the neuromuscular blocking actions and reversals of metocurine in 14 adult cats, either sex, weighing 2.5-4.5 kg. Ligation of both renal pedicles in 6 cats (Group II) and its sham operations in 8 cats (Group I) were done under the pentobarbital anesthesia. Neuromuscular monitoring was done using a common peroneal nerve-tibialis anterior muscle preparation. The mean blood pressures, acid-base status and serum electrolytes at the time of injection of metocurine or neostigmine were not significantly different between two groups. The heart rates at the administration of neostigmine were significantly decreased probably due to the decreased body temperatures in group I. The onset time of metocurine with 3 X ED95 in acute renal failure was simiiar to that in normal renal function. However, the duration of metocurine with 3 X ED95 in acute renal failure was significantly longer that that in normal renal function. The effeets of neostigmine administered at 15%-spontaneous twitch recovery for the recovery indices and antagonism effects were not significantly different between two groups. In conclusion, acute renal failure prolongs the duration of metocurine, but not interfere its onset. Additionally, there is no effect on the reversal actions of neostigmine if administered at the spontaneous recovery of twitch height more than 15%.