Cutaneous touch-pressure, vibration, and thermal cooling detection thresholds were estimated on the skin of one foot for 80 patients with motor neuron disease (MND) and compared with that of more than 300 site, age, and sex-matched healthy controls. Fourteen of the patients had elevated thresholds (greater than or equal to 95th percentile): 7 showed elevated thresholds of sensitive points, 5 an increased number of insensitive grid points, and 2 a combination of these criteria. Therefore, raised vibration thresholds occur more frequently in MND patients than in controls (p less than 0.001). A detection threshold abnormality was not demonstrated for touch-pressure or for thermal cooling. These results are in keeping with the demonstrated increased cutaneous myelinated fiber degeneration in this condition and with evidence of sensory neural system involvement at postmortem examination. Although motor neurons are selectively vulnerable in MND, afferent neurons may also be affected, albeit less frequently and/or to a lesser degree.