An automated system, incorporating the ANOPS-101 mini-computer, has been used to analyse the EMG. The vastus medialis (VM) and biceps brachii (BB) muscles were studied in 28 controls, 16 patients with myopathies, and in 26 patients with denervating disorders. For each muscle mean values were computed for the durations and numbers of phases of muscle action potentials; the mean density and amplitude of the deflections in the interference pattern were also measured. A higher incidence of abnormalities could be detected in myopathic than in neuropathic disorders; for both conditions the incidence was significantly greater in BB than in VM. For the diagnosis of denervation the most useful measurement was that of potential duration; for the detection of myopathies amplitude determinations were also very useful. The present results have been compared with those of other published studies in which automatic EMG analysis has been employed.