The term "mural cell" designates the nonendothelial cells such as we see in the retinal capillaries. It is specific and descriptive, and does not invoke the ambiguities which surround the term pericyte. Although the mural cells are probably contractile and probably control flow through the maze of capillaries, their function has not been clearly established. They are especially vulnerable in diabetic retinas but interpretation of pathologic changes must distinguish between senile, diabetic, and artifactual abnormalities.