Anaemia is a frequent symptom in children with chronic uraemia. There is only few information about haemopoietic committed stem cell functions in renal insufficiency. Therefore we tested the ability to form granulopoietic and erythropoietic cell colonies in vitro in children with chronic uraemia.Following separation of mononuclear cells fron bone marrow aspirates by Ficoll Isopaque gradient centrifugation granulopoietic precursor cells were stimulated in soft agar gel using feeder layers of normal human leukocytes as source of colony stimulating factors. Erythropoietic precursor cells were stimulated in plasma clots by erythropoietin. The cells were identified by staining methods (Pappenheim respectively Lepehne) and counted.Quantity and proliferative capacity of isolated granulo-poietic and erythropoietic stem cells were not suppressed in the tested children. Under in vitro conditions the responsiveness of erythroid precursor cells to erythropoietin seemed to be normal. After adding autologous serum different degrees of inhibition of colony formation of erythropoietic stem cells resulted. The observed existance of inhibitory activity in sera of uraemic children may be one important factor in the pathogenesis of anaemia in chronic renal failure.