Chronic anemia of cancer can be corrected in approximately 50% of the cases by treatment with recombinant human erythropoietin (rHuEPO). Early prediction of responsiveness would avoid the emotional and financial burden of ineffective medical intervention. Eighty patients with chronic anemia of cancer undergoing treatment with rHuEPO (150 U/kg, 3 times per week by subcutaneous injection; after 6 weeks without response, 300 U/kg) participated in this study. Response was defined as a gain of at least 2 g/dL hemoglobin (Hb) within 12 weeks. Multivariate discriminant analysis and logistic regression analysis of response were performed on routine blood tests; serum levels of EPO, iron, ferritin, transferrin, and its receptor; World Health Organization (WHO) performance status; various cytokines; neopterin; stem cell factor; C- reactive protein; and alpha 1-antitrypsin. At baseline, none of these factors showed sufficient prognostic power. The following predictive algorithm was developed: (1) If after 2 weeks of therapy both the serum EPO level is > or = 100 mU/mL and Hb concentration has not increased by at least 0.5 g/dL, unresponsiveness of the patient is very likely (predictive power, 93%); otherwise, response may be predicted with an accuracy of 80%. (2) If both the serum level of EPO is less than 100 mU/mL and Hb concentration has increased by > or = 0.5 g/dL, response is highly probable (predictive power, 95%). (3) Alternatively, a serum ferritin level of > or = 400 ng/mL after 2 weeks of rHuEPO therapy strongly indicates unresponsiveness (predictive power, 88%), whereas a level less than 400 ng/mL suggests response in 3 of 4 patients.