Sideroblastic erythropoiesis is a recognized complication of acute alcoholism1 and disturbances in porphyrin synthesis have been reported in sideroblastic anemia2. In order to investigate the mechanism of alcoholic-induced sideroblastic erythropoiesis coproporphyrin (C.P.) and protoporphyrin (P.P.) levels were measured in 26 patients admitted with acute alcoholism. Bone marrow examination showed that 11 patients had ring sideroblasts, while in 15 other patients there were adequate iron stores, but no ring sideroblasts. The red blood cell (C.P.) and (P.P.) levels were elevated in all of the 11 patients with ring sideroblasts, but in only three out of the 15 patients with no ring sideroblasts. These data clearly separate those patients with a disturbance of mitochondrial iron metabolism and increased erythrocyte porphyrins from other patients suffering from a comparable degree of alcoholism in whom neither abnormality appeared to exist. We conclude therefore that alcoholic sideroblastic erythropoiesis probably reflects ethanol-induced disturbance in the heme synthetic pathway.