Twelve severely emaciated patients with emphysema and 4 control patients with mild emaciation were studied. Arterial blood gas analysis, pulmonary function tests, and muscle biopsy were performed. According to the percentage of ideal body weight (%IBW), patients were divided into two groups of 6 patients each; one with %IBW values greater than 70.0 (group 1) and the other with %IBW values less than 70.0 (group 2), and 4 control patients with emphysema whose %IBW values were greater than 85.5. %FEV1.0, PaO2 and Hugh-Jones scores in group 2 patients were consistent with significantly greater deterioration as compared with those in group 1 patients and controls. In the muscle fibers of 11 patients and 4 controls, nicotinamide and adenosine dinucleotide tetrazolium reductase activity was studded with spots. Nemalin rods were detected in 3 specimens in group 2 and in 1 specimen each in both group 1 and controls. These changes probably result from chronic hypoxemia. Fiber type grouping accompanied by type II dominant fiber atrophy was demonstrated in 5 patients of group 2, whereas type II fiber atrophy was shown in 2 specimens from patients of group 1. Diameters of both types I and II fibers in group 2 were smaller than those in group 1 and controls. Significant correlations were observed between fiber diameters and %IBW, %FEV1.0 and %IBW, and PaO2 and %IBW. Neurogenic and disuse muscular atrophy due to both hypoxic axonal disorder and disuse is likely to be the cause of the emaciation, and a 'vicious circle' between muscular atrophy, respiratory function and hypoxemia probably exists in group 2. Since mild or moderate emaciation was observed in controls and group 1 in spite of the lack of fiber atrophy, involvement of fat and connective tissue should also be taken into consideration to determine the cause of emaciation.