The interaction between ketamine and various neuromuscular blocking drugs is presently unclear. Therefore, experiments were carried out on rabbits to determine ketamine's effect upon the neuromuscular blockade produced by succinylcholine (SCh), d-tubocurarine (d-TC), pancuronium and a new short-acting drug, AH 8165, an azobis-arylimidazo-(1,2-a) pyridinium dihalide. The results of these experiments indicate that ketamine at a dose of 15 mg/kg, i.v. had no muscle blocking action of its own, but did cause a 10% increase in the muscle twitch height. When ketamine was given prior to SCh, the depth of SCh blockade was significantly increased compared to the SCh blockade alone. Ketamine was without effect upon the depth of the pancuronium, d-TC and AH 8165 neuromuscular block. p Recovery slopes of the SCh, pancuronium, d-TC and AH 8165 blocks were unaffected by the ketamine administration. These results support the concept that ketamine facilitates the action of depolarizing blocking drugs and has no effect upon the non-depolarizing neuromuscular blocking drugs.