The effect of diminazine aceturate (Berenil ) on the neuromuscular transmission was studied. On the chick biventor cervicis muscle, dimin azine augmented the indirectly elicited muscle twitches and the contrac ture induced by carbachol on this avian muscle. On the rat diaphragma tic muscle, higher doses of the drug produced partial neuromuscular blockade which was potentiated by the addition of neostigmine. Dimin azine aceturate augmented the indirectly elicited muscle twitches of the upper lip muscles of anaesthetised dogs, rabbits and guinea pigs followed by partial neuromuscular blockade, meanwhile, it induced paralysis of the tibialis muscle of rabbits. Diminazine potentiated the inhibitory effect of succinyl choline on the upper lip muscles of anaesth etised dogs. It could be concluded that Diminazine aceturate affected the neuromuscular transmission with a depolarizing action.