The clinical and laboratory findings in three patients with primary acquired sideroblastic anemia (PASA) are described. The results demonstrate that what seems to be a well defined entity of the large group of sideroblastic anemias, is in itself a heterogeneous subgroup, with differences capable of detection by more extensive studies. Electron microscopic examination of erythroid cell precursors confirmed previously described features such as deposition of large amounts of iron, mainly in the mitochondria. The precipitated serum proteins revealed an increased content of ferritin molecules only in the patients and not in control individuals, suggesting an increased supply of iron to the erythroid precursors. This finding could serve as an additional mechanism for the accumulation of iron in the erythroid precursors, considering also the defect in heme synthesis and increased permeability of the erythroid membrane for iron, described in this condition.