By examining sideroblasts in normal subjects and in patients with various hematologic disorders and determining the rates of appearance, a sideroblastogram consisted of classifications of types I, II and III, according to numbers of iron granules was made. Again, sideroblast ratios (S. r.) were computed and studies were carried out by comparing the proportion of sideroblasts with serum iron. The results are as follows: 1) The proportion of sideroblasts has been found extensively in the normal persons, but in the sideroblastogram it is all intermediary in type, whose sideroblast ratio never exceeds 1 nor yields zero. 2) The proportion of sideroblasts in the cases of erythropoietic disturbances in the bone marrow such as hypoplastic anemia, leukemia, disorders due to irradiation has been found generally high, and in almost all these cases the proportion of sideroblasts reveals a shift to the right in the sideroblastogram at the same time S. r. has been above 1. 3) In various iron deficiency anemias in a broader sense, the proportion of sideroblasts is decreased and a shift to the left is demonstrated in the sideroblastogram; and S. r. is zero or is approaching to zero. 4) On the other hand, in Graves' disease and kala-azar the proportion of sideroblasts is normal, but in hemolytic anemia, liver cirrhosis and chronic nephritis it is high. Again, in agranulocytosis and myxedema the proportion of sideroblasts is low. 5) Sideroblasts seem to have some relationship with serum iron, but the two do not necessarily change parallel with each other. 6) These procedures of the determining of sideroblasts are equally useful or even superior to similar methods on serum iron in the differentiation of various anemic patients. 7) From these results, it is believed that stainable iron in these sideroblasts exists between serum iron and hematopoiesis in the process of utilization, and that it naturally has a close association with both serum iron and hematopoiesis. Note: Sideroblasts are the erythroblasts containing stainable, nonhemoglobin iron granules.