Forty-seven men with numbness and paresthesiae in their hands after long-term occupational exposure to vibrating hand-held tools were examined neurophysiologically and clinically. The vibration thresholds of the finger tips were assessed and fractionated neurography of the median nerve motor and sensory fibres carried out. They were compared with control groups of healthy subjects and patients with idiopathic carpal tunnel syndrome. The patients exposed to vibration had major increases in their finger vibration thresholds, shown with both the Goldberg-Lindblom vibrameter and the Lundborg vibrogram. They also had a moderately increased motor distal latency at the wrist, but significantly less than patients with idiopathic carpal tunnel syndrome. Similar changes were seen in the sensory conduction velocities from finger to wrist. Measurement of fractionated conduction velocity across the carpal tunnel showed a bimodal distribution; one group of patients exposed to vibration had a significant reduction in conduction velocity similar to that in the genuine carpal tunnel syndrome, and one group had no localised affection at the carpal tunnel, suggesting more distal dysfunction at the level of palm or finger, or at the receptor level. A careful neurophysiological assessment of these cases is necessary before treatment is planned. It is particularly important to confirm median nerve damage at the wrist level if the carpal tunnel ligament is to be sectioned.