Capillaries of the skin have been thought to be of a nonfenestrated type according to studies of previous investigators. However, the present study revealed that fenestrations exist in the endothelium of cutaneous vessels. Capillary fenestrations are numerous in the human finger and the mouse sole and are moderately frequent in the guinea pig sole and ear. In the skin of the human chest, however, they are rarely encountered. Sometimes, endothelial fenestrations are encountered in venules as well.