Recent progress on the isolation and culture of capillary endothelial cells has allowed comparison of the biochemical and physiologic properties of endothelial cells from large and small blood vessels. These cells share certain common features including monolayer formation, production of Factor VIII antigen, production of prostacyclin, and presence of Weibel-Palade bodies. Endothelial cells from capillaries, however, differ from the endothelial cells of large arteries and veins in their nutritional requirements and in their responses to growth and migration stimuli. The differences found between endothelial cells from large and small blood vessels underscore the importance of using cells derived from vessels of appropriate size when studying the macro- and microangiopathies associated with diabetes.