Neuromuscular disorders of varying aetiology frequently lead to respiratory failure. This situation contrasts with the rare application of suitable tests of pulmonary function in this group of patients. As a result, respiratory complications are not detected until they have progressed to a terminal stage. With the sequential measurement of vital capacity, and a determination of the maximum inspiratory and expiratory pressures (PImax and PEmax), we have reliable and practicable diagnostic measures available that permit the recognition of respiratory failure at an early stage. This fact is of particular importance, since the application of modern ventilation techniques in suitable patients can make a substantial contribution towards both improving the patient's quality of life and prolonging it.