The incidence and characteristics of ring sideroblastic and megaloblastic changes in bone marrow were studied in chronically ill, malnourished alcoholics and well-nourished alcoholics without complicating medical illness. A clear correlation of blood alcohol level with changes in serum pyridoxal-5-phosphate (PLP) values or with the incidence of ring sideroblasts could not be demonstrated. The appearance of ring sideroblasts was associated with dietary restrictions of pyridoxine and noticeable folic-acid-deficient megaloblastosis. The majority of subjects with ring sideroblasts were from the chronic, malnourished alcoholic group; the number of sideroblasts correlated with severity of marrow magaloblastic change. While low serum PLP levels were characteristic of the chronically ill alcoholic with ring sideroblasts, equally low levels were detected in the absence of the marrow abnormality. Thus, a low serum PLP value alone is not a certain indication of the presence of marrow ring sideroblasts.