A method is described for the automatic analysis of EMG interference patterns obtained at optional non-controlled force levels. It is a modification of Willison's method of measuring turns and amplitude of the signal. In the method, the mean amplitude is plotted against turns obtained during 300 msec for each of 20 recording sites. Different voluntary strengths are used and a scatter of points is obtained. Confidence limits enclosing these points are constructed for healthy subjects for 4 different muscles with concentric and monopolar electrodes. The normal values differ with age, muscle, sex and electrode. The method is tested on patients with myopathic or neurogenic EMG and a high diagnostic yield is obtained. The method is objective, reproducible, fast and needs relatively small computer facilities.