Erythropoietin (Epo) is the primary growth factor involved in the regulatio
n of erythropoiesis and was once thought to be unique to the hematopoietic
system. Like other cytokines that have been discovered in one system, only
then to have unrelated functions attributed to it, Epo has now been found t
o have nonerythropoietic effects. These effects are mediated by Epo binding
to its specific cell surface receptor. Functional Epo receptors are presen
t on many nonerythropoietic cell types. This article reviews the cell types
on which the Epo receptor is found, and the nonerythropoietic functions th
at can be attributed to Epo. Emphasis is placed on the vascular, gastrointe
stinal, and neurologic effects of Epo.