In three patients with lesions of peripheral regions of the central nervous system and paralyses of the respiratory muscles (malignant myasthenia, amyotrophic lateral sclerosis and residual manifestations after poliomyelitis), artificial ventilation has been performed continuously for periods from 7 years 4 months to 18 years 9 months using some degree of hyperventilation (PCO2 19.5--26.8 mmHg). The mechanics of breathing were studied by pneumotachography with synchronous recording of transpulmonary and oesophageal pressures using cuffed tubes. The findings were a decrease of total compliance of the respiratory apparatus (Ctot 23--28 ml x cm x H2O-1), a severe decrease in compliance of the lung tissue (CL 24--30 ml x cm x H2O-1), a sharp increase of bronchial resistance during inspiration (RresLI 15.0--23 cm x H2O l-1 s-1), and during expiration (RresLE 16.5--30.7 cm x H2O l-1 s-1), an elevation of compliance of the chest (Cw 358--555 ml x cm x H2O-1), a reduction of non-elastic resistance of the chest (Rres w 0.2--0.6 cm x H2O l-1 s-1). These parameters indicated progressive changes of the structures of the lung tissue and of the tracheobronchial tree which were most pronounced in the case of amyotrophic lateral sclerosis.