Sensory nerve function was determined in 19 patients with amyotrophic lateral sclerosis (ALS), using a battery of clinical and neurophysiological tests. This assessment was repeated on 12 patients after intervals of 6-18 months. Twelve controls were also studied. In the ALS group, only 2 patients had noticed mild sensory symptoms and none had sensory signs. Between successive studies the vibration thresholds increased, but not to a significant degree. ALS patients showed a significant fall in amplitude of the sensory nerve action potentials in the median, radial, and sural nerves (P < 0.04); sensory nerve conduction velocity did not alter. The median nerve somatosensory evoked potential N19 latency showed a highly significant increase (P < 0.008). Significant subclinical deterioration in sensory nerve function occurs in ALS, and parallels the progressive motor decline. Neuronal degeneration in ALS is not restricted to motor neurons.