Clinical and neurophysiological studies were conducted in 47 patients with chronic obstructive airways disease and compared with 46 age-matched control subjects. Symptomatic neuropathy was reported in 13% and ankle jerks were absent in 45% of hypoxic patients. Peroneal and median nerve conduction velocities and median and sural sensory nerve amplitudes were significantly reduced in hypoxic patients (p less than 0.01). Six hypoxic patients underwent biopsy of the sural nerve, soleus muscle and overlying skin. Nerve glucose, sorbitol, fructose and myo-inositol concentrations were normal. Detailed light and electronmicroscopy revealed both nerve fibre and microvascular pathology. Segmental demyelination (32%) and unmyelinated fibre degeneration were found to be prominent lesions. The sural nerve perineurium was thickened due to an increase in the number of perineurial lamellae and an increase in intraperineurial space. Basement membrane thickening was observed in capillaries of nerve, muscle and skin. Endothelial cell hyperplasia and hypertrophy were observed in nerve and muscle capillaries but not in skin capillaries. In conclusion, this study has provided neurological, neurophysiological and neuropathological evidence of a neuropathy in hypoxic patients with chronic obstructive airways disease. These findings may be of relevance to some aspects of the aetiology of human diabetic neuropathy.