The interaction of gallamine, 20 mg, and the interaction ofd-tubocurarine, 3 mg, with succinylcholine, 1 mg/kg, were studied in 25 patients during nitrous oxide-oxygen-meperidine anesthesia. In five patients given three successive doses of succinylcholine separated by intervals of 10 and 20 minutes, no differences in times to onset, magnitudes of twitch-height depression or times of 80 per cent recovery of neuromuscular transmission were found. Prior administration ofd-tubocurarine to ten patients and gallamine to another ten patients did not alter the times to onset or magnitude of twitch-height depression produced by the third dose of succinylcholine. Although mean time to 80 per cent recovery of twitch height after administration of succinylcholine was not significantly altered by gallamine, it was shortened by rf-tubocurarine from 10.9 ± 0.5 (SE) minutes to 8.9 ±0.4 minutes. In all patients, ability to sustain tetanus and absence of posttetanic facilitation indicated the absence of desensitizing neuromuscular block. It is concluded that prior administration of either gallamine or d-tubocurarine in the dose studied has little effect on the magnitude or type of neuromuscular blockade produced by suecinylcholine.