The effect of tubocurarine and suxamethonium on directly and indirectly elicited contractions of skeletal muscle in unanaesthetized man using single and train of four impulses.

1 Contractions of adductor pollicis in unanaesthetized man were elicited by direct and indirect stimulation. Single twitch responses as well as those by a train of four impulses at 2 Hz for 2 s were elicited for indirect stimulation. 2 After a suitable control period, tubocurarine (0.05 mg/kg) or suxamethonium (0.08 mg/kg) was administered intravenously. 3 A stepwise diminution in the train of four impulses was noticed after tubocurarine. Indirectly elicited contractions due to single stimulus and direct muscle stimulation remained unaltered. 4 Partial blockade of transient duration occured after suxamethonium for single as well as train of four stimuli. Directly elicited contractions remained unchanged. The intensity of blockade depended on the rate of injection of suxamethonium. 5 Indirectly elicited contractions by train of four impulses is a reliable and sensitive method for testing neuromuscular blocking drugs in unanaesthetized man.