Cumulative d-tubocurarine dose—response curves were determined in 35 unpremedicated adult surgical patients. In five awake patients with and five awake patients without ulnar nerve block the median effective doses of d-tubocurarine necessary for 50 per cent depression ot twitch tension (ED30) were S.3 and 9.1 mg/m2, respectively, The presence or an ulnar nerve block did not significantly alter ED50, which suggests that the central nervous system has little influence on the d-tubocurarine dose-response curve. The ED50's of d-tubocurarine were 4.8, 4.5, 2.5, 3.2, and 3.8 mg/m2in patients anesthetized with 1.0 to 1.3 per cent alveolar concentrations of halothane for 10, 20, 40, 80, and 160 minutes, respectively. It is concluded that duration ot anesthesia has no effect on neuromuscular blockade by d-tubocurarine.