Oxymetholone, a steroid of proven clinical value in the treatment of refractory anemia, was without effect on endogenous or erythropoietin-mediated heme synthesis in fetal mouse liver cell cultures. This conclusion applied both when the cells were exposed to oxymetholone prior to culturing with erythropoietin and when the steroid was present in the cultures simultaneously with erythropoietin. Unlike those steroids having a direct effect on erythroid cells, oxymetholone also failed to increase the proportion of erythropoietin responsive cells in DNA synthesis. The relevance of these observations to the therapeutic benefit of oxymetholone is discussed. While the possibility that oxymetholone has to be metabolized to an active form cannot be excluded, the results suggest that oxymetholone does not seem to be erythropoietically active by a direct effect on erythroid cells. The fact that it is a successful therapeutic agent in some patients with aplastic anemia may be due to its proven ability to increase endogenous erythropoietin levels or to reduce ineffective erythropoiesis.