Electrical stimulation of the digital nerves of the index finger produces changes in the EMG signal during steady voluntary contraction of the first dorsal interosseous muscle. This electrocutaneous reflex (ECR) was studied in 90 patients classified into different categories according to diagnostic criteria for multiple sclerosis. In addition, pattern reversal visual evoked responses (VER), brainstem auditory evoked responses (BAER) as well as spinal and scalp recorded somatosensory evoked potentials (SSEP) were investigated by stimulating both the index finger and the posterior tibial nerve. The reflex response was altered uni- or bilaterally in 56 per cent of the patients and the abnormalities of the ECR were related to the categories of diagnostic probability. Pathological results were found in 28 per cent of the hands without clinical evidence of sensorimotor deficit. Although ECR abnormalities were often associated with clinical signs, significant correlation was found only with hyperreflexia and/or increased muscle tone in the corresponding upper limb. Pathological ECR were more common than pathological SSEPs with finger stimulation recorded under identical stimulus conditions. Fewer abnormalities were found by ECR testing than with VER, but the proportion of abnormal ECR was higher than that of BAER. ECR provides a valuable supplement to existing electrophysiological procedures for detecting lesions in the central nervous system.