High levels of CD36 expression are found in triglyceride storing and secreting cells such as differentiated adipocytes and mammary secretory epithelial cells and in some capillary endothelial cells. We have found high levels of CD36 in the capillary endothelium of murine adipose tissue and in cardiac and skeletal muscles. Muscle cells themselves were CD36 negative. No CD36 was found in brain endothelium. Cardiac and skeletal muscle tissues are highly oxidative and catabolize long-chain fatty acids as a source of energy while brain tissue does not use long-chain fatty acids for energy production. Since capillary endothelial cell CD36 expression appeared to correlate with parenchymal cell fatty acid utilization and since CD26 has been identified recently as a long-chain fatty acid-binding protein, we examined heart tissue CD36 expression in murine models of insulin-dependent (nonobese diabetic, NOD) and non-insulin-dependent diabetes mellitus (KKAY). Diabetic NOD and KKAY mice had serum triglyceride levels 2.6- and 4.2-fold higher, respectively, than normal mice and exhibited 7- and 3.5-fold higher levels of heart microsomal CD36, respectively, than control mice. Mice fed a 40% fat diet expressed heart tissue CD36 at a level 3.5-fold higher than those fed a 9% fat diet. These data suggest that endothelial cell CD36 expression is related to parenchymal cell lipid metabolism.