The efficacy of monitoring neuromuscular blockade during surgery based on visual assessment of the response to calf stimulation was determined in twenty-five patients. The calf stimulator was adjusted before the administration of any muscle relaxant to produce a brisk ankle jerk. Following an initial bolus dose of atracurium (0.5 mg/kg), further incremental doses (0.2 mg/kg) were administered when the response to calf stimulation was small and obvious. The resultant neuromuscular blockade was judged to be adequate throughout the surgical procedures, with an average of five incremental doses of atracurium being administered. In the presence of neuromuscular blockade the response to calf muscle stimulation was often greater than that produced by supramaximal stimulation of the ulnar nerve with a peripheral nerve stimulator. The response to calf muscle stimulation often persisted after that resulting from ulnar nerve stimulation was abolished. The technique has only limited accuracy in assessing neuromuscular blockade. However, it may be useful in helping to avoid the wide fluctuations in blockade which are prone to occur with the intermediate duration competitive neuromuscular blocking agents.