In the present study, we tried to detect ferritin-secreting cells (FSC) as plaque-forming cells using a reverse hemolytic plaque assay and thereby to evaluate some of the cellular aspects of ferritin dynamics associated with various hematological disorders. Healthy adult males had 433 FSC and adult females had 244 FSC in 1 × 105 peripheral blood mononuclear cells (PBM). The mean numbers of FSC in 1 × 105 lymphocyte-enriched fraction were 120 in males and 53 in females, and those in 1 × 105 monocyte-enriched fraction were 932 in males and 668 in females. These results indicate that monocytes contain about 8–13 times as many FSC as lymphocytes. Each fraction of PBM from patients with iron deficiency anemia contains only about half as many FSC as those of normal individuals. Whereas, in states of increased iron storage such as seen in sideroblastic anemia, aplastic anemia and myelofibrosis, the mean numbers of FSC are markedly increased to about 4–8 times in PBM, about 11–20 times in lymphocytes and about 3–7 times in monocytes, compared with each counterpart of the normal i