The prevalence of clinical and electrophysiological signs of peripheral nerve disease was evaluated in 151 patients with chronic obstructive pulmonary disease. Patients with concomitant disorders affecting the peripheral nervous system were excluded. Thirty patients had clinical signs of a mild sensorimotor and distal neuropathy and 13 additional patients had only electrophysiological abnormalities. The rate and the severity of the neuropathy correlated with the severity of chronic hypoxaemia. Three out of 20 patients with mild hypoxaemia (PaO2 less than 15 mm Hg below normal) had polyneuropathy as compared with 15 out of 36 with severe hypoxaemia (PaO2 more than 30 mm Hg below normal (rates different at the 10% level)). PaO2 and age were the only variables discriminating between patients with and without peripheral neuropathy.