Defective iron metabolism, mild haemolysis and impaired erythropoiesis contribute to the anaemia of chronic disorders (ACD), but evidence for a deficiency of circulating erythropoietin (Epo) is equivocal. We have examined serum Epo in moderately anaemic patients with Hb less than 10 g/dl--41 patients with ACD (23 associated with rheumatoid disease and 18 with malignancy), 17 with uncomplicated iron-deficiency anaemia and 33 with chronic renal failure (CRF). In ACD the serum Epo (mean (confidence limits] results of 41 (31, 54) mU/ml for the rheumatoid group and 63 (49, 80) mU/ml for the malignancy group, were significantly lower than the Epo of 104 (78, 136) mU/ml for the iron-deficiency group. The CRF group with more severe anaemia had serum Epo of 27 (19, 35) mU/ml. Thus, recombinant human erythropoietin (rHu Epo) should be considered for the treatment of ACD associated with rheumatoid disease and malignancy.