Studies in experimental animals indicate that chronic increases in neural drive to limb muscles elicit a fast-to-slow transformation of fiber-type proportions and myofibrillar proteins. Since neural drive to the parasternal intercostal muscles (parasternals) is chronically increased in patients with severe COPD (COPDs), we carried out the present study to test the hypothesis that the parasternals of COPDs exhibit an increase in the proportions of both slow fibers and slow myosin heavy chains (MyHC). Accordingly, we obtained full thickness parasternal muscle biopsies from the third interspace of 7 COPDs (mean age 59±SEM 4 years) and 7 age-matched controls (AMCs). Fiber typing was done by immunohistochemistry and MyHC proportions were determined by SDS-PAGE followed by densitometry. COPDs exhibited higher proportions of slow fibers than AMCs (73±4% versus 51±3%; p<0.01). Additionally, COPDs exhibited higher proportions of slow MyHC than AMCs (56±4% versus 46±4%, p<0.04). We conclude that the parasternal muscles of patients with severe COPD exhibit a fast-to-slow transformation in both fiber type and myosin heavy chain proportions. Previous workers have demonstrated that remodeling of the externals intercostals-another rib cage inspiratory muscle-elicited by severe COPD is characterized by a slow-to-fast transformation in both fiber types and MyHC isoform proportions. The physiological significance of this difference in remodeling between these two inspiratory rib cage muscles remains to be elucidated.