Serum ferritin level has been shown by many investigators to be a good indicator of bone marrow iron stores in normal subjects. Although this correlation may hold in some pathological situations, it is lost in others. In leukemia a dissociation has been observed between serum ferritin levels and bone marrow iron stores. Leukemic cells were demonstrated to contain high levels of ferritin and to secrete it in the serum, causing this dissociation. In this study we investigated the possibility of having an analogous situation in patients on chronic hemodialysis. The latter patients have normal or high ferritin levels irrespective of bone marrow iron stores. Our results show that blood neutrophils and lymphocytes do not contribute to the high serum ferritin levels in these patients. Ferritin level in blood monocytes, however, was found to correlate with the serum ferritin levels and bone marrow iron stores in dialysis patients. Hence we concluded that sources other than blood leukocytes must be contributing to the high serum ferritin level in these patients. On the other hand, to unravel the role played in these changes by the monocytic cell population requires dynamic studies.