Nineteen patients with chronic respiratory insufficiency, mean age 61.4 +/- 12.2, have been investigated with pulmonary function tests, clinical neurological examination and neurophysiological methods including motor and sensory conduction studies and needle electromyography. None of them had conditions known to affect the peripheral nervous system such as diabetes, alcoholism, or uraemia. The motor and sensory conduction studies showed only a reduced mean amplitude of the ulnar nerve SAP and of the compound muscle action potential of the APB and EDB muscles. The EMG was abnormal in 94.7% of the cases and showed an increased percentage of polyphasic potentials and a reduced recruitment pattern of motor units firing at high frequency. The data seem to support the hypothesis of an involvement of motor neurons in this condition although the evidence for a neuropathy is lacking.