Simultaneous measurements of tetanic and single twitch contractions of the adductor politics muscle in man were made during neuromuscular blockade induced by suxamethonium (0.2 mg/kg) under nitrous oxide, oxygen and pentazocine anaesthesia. 2. After a suitable control period, suxamethonium (0.2 mg/kg) was given intravenously and the same dose was repeated 15 min later. After a further 15 min gallamine (0.2 mg/kg) was administered intravenously. When recovery from gallamine reached a plateau on the tetanic contraction recording a third injection of suxamethonium was given. 3. In most patients, suxamethonium (0.2 mg/kg) caused a partial blockade of the single twitch and complete blockade of the tetanic contraction. In every instance, the tetanic contraction was more depressed and recovered more slowly than the single twitch which not only recovered promptly but also showed overshoot. 4. After gallamine marked antagonism to suxamethonium block developed and this was greater with the single twitch than with the tetanic contractions. 5. Tetanic-tension fade was observed after every injection of suxamethonium and the degree of fade was dependent on the frequency of the tetanic stimulation.