PURPOSE: Metabolic abnormalities and increased sedentary time in maintenance hemodialysis (MHD) patients lead to unfavorable skeletal muscle adaptations and reduced exercise tolerance. Muscle function is affected by the proportion of “pure” myosin heavy chain (MyHC) fiber type isoforms (Type I, IIa, and IIx) and prevalence of co-expressing “hybrid” fibers (Type I/IIa, IIa/IIx, I/IIa/IIx, and I/IIx) which display unique functional/metabolic properties associated with disease and inactivity. Previous investigations have utilized ATPase fiber typing methods in MHD patients, but this technique lacks fidelity to identify hybrid fibers. The purpose of this study was to 1) more accurately measure MyHC fiber type distribution in older men undergoing MHD and 2) compare the MyHC fiber type profile of these MHD patients to the literature. METHODS: Seven subjects (6 males and 1 female) receiving MHD treatment (age: 63.6 ± 4.4y; MHD duration range: 0.8 - 10y) underwent resting vastus lateralis muscle biopsies. Individual muscle fibers were mechanically isolated (696 total fibers) for MyHC fiber typing via SDS-PAGE. RESULTS: MyHC fiber type distribution was 31% I, 4% I/IIa, 23% IIa, 27% IIa/IIx, 3% I/IIa/IIx, 2% I/IIx, and 11% IIx. Rarely identified MyHC I/IIx fibers were found in two MHD patients. CONCLUSIONS: MyHC fiber type distribution was 31% I, 4% I/IIa, 23% IIa, 27% IIa/IIx, 3% I/IIa/IIx, 2% I/IIx, and 11% IIx. Rarely identified MyHC I/IIx fibers were found in two MHD patients.