This study demonstrated that there was interanimal and interregional variability of proportions and sizes of the muscle fiber types in the hamster diaphragm. Muscle fiber type proportions and sizes were determined for each side (right, left), surface (abdominal, thoracic), and region (sternal, anterior costal, posterior costal, crural) in six hamsters. There was marked regional and surface-to-surface variability and some interanimal variability in proportions and sizes of fiber type within the hamster diaphragm. The sternal and costal regions were relatively homogeneous. However, there were differences in both proportions and sizes of fiber types between the thoracic surface of the crural region and the abdominal surface of the crural region. These two surfaces of the crural region differed from the rest of the diaphragm. For muscle fiber type proportions, type 2a fibers demonstrated the most interanimal variability. Muscle fiber size varied little between animals.