The diaphragm may differ from other skeletal muscles in certain blood flow characteristics. We attempted to determine if this could be accounted for by structural differences in the microvasculature. We compared coded specimens of the diaphragm to the intercostals and triceps in rats by a cast corrosion, scanning electron microscopic study. For the comparison we first quantitatively described the vasculature by measuring the angles, distances, and diameters. We also tabulated subjective, descriptive, recurring patterns. We then performed frequency analysis by vessel diameter, correlation, and factor analysis to obtain the description. Arteries and veins of greater than 50 microns diameter have structural characteristics of a conducting system, namely, infrequent, single branching at obtuse angles whereas the vessels from about 15 to 50 microns in diameter have greater branching and frequently splay into many smaller streams. The capillaries form arcades and dichotomize with Y- and psi-shaped branches. The best predictor of branching (distance, angle, and pattern) is the trunk diameter. Individual and combinations of measurements and patterns comparing the diaphragm to the triceps and intercostals pointed out no convincing difference in these structural aspects of microvasculature of these muscles.