In normal subjects, somatosensory evoked potentials(SEPs) were produced by increases or decreases of the load on the biceps muscle during voluntary contraction. The stimuli lasted only 20 msec and caused less than 2° of elbow flexion or extension. When the stimulus was applied during voluntary movement of the elbow, the SEP was attenuated, and the subject was less able to discriminate between loading and unloading pulses. In each of eight subjects, there was a positive correlation between the percentage of correct responses and the size of the SEP. The measurement of both SEPs and perceptual accuracy under various test conditions provides a refined technique for studying the relations between electrical events and sensory processes.