To examine the relationship between nutrition, pulmonary function, respiratory muscle strength, and respiratory muscle morphometry, we compared physiologic data and muscle morphometry obtained from internal intercostal, external intercostal, and latissimus dorsi muscle biopsies in 68 patients who were having a thoracotomy. We stained the biopsies for myosin ATPase and measured the proportions and diameters of the type 1 and type 2 fibers. There were more qualitative changes in the external intercostal muscles than in the other two, and some of these changes related to the incidence of malignancy. There were more type 1 fibers in the external intercostal (64 +/- 10 percent) and internal intercostal muscles (59 +/- 12 percent) than in the latissimus dorsi (44 +/- 13 percent) (p less than 0.005). The mean diameter of the type 2 fibers in the external intercostal muscles was less (44 mu +/- 7 mu) than the diameter in the latissimus dorsi (51 mu +/- 9 mu) and the internal intercostal muscles (52 mu +/- 8 mu) (p less than 0.01). The diameters of both fiber types were greater in men than in women. There was no significant relationship between measures of pulmonary function or respiratory muscle strength and muscle fiber proportions and diameters. There were significant correlations between the percentage of ideal body weight and type 1 and type 2 fiber diameters. We conclude that sex and nutrition influence respiratory muscle morphometry.