Recombinant human erythropoietin (rHuEPO) improves chronic anemia of cancer, but the proportion of patients who respond favorably to the treatment varies depending on the type of neoplasia. Preliminary data of the two malignancies with the highest response rates, namely, multiple myeloma and squamous cell carcinoma, are reported. Twenty patients with multiple myeloma and 14 with squamous cell carcinoma, who had presented with hemoglobin levels <11 g/dl, were treated with rHuEPO, 150 U/kg, three times/week. Response, defined as an increase of at least 2 g/dl hemoglobin within 12 weeks, was achieved by 15 myeloma patients (75%) and 11 patients with squamous cell carcinoma (79%). Tolerance of the treatment was excellent. The WHO performance status and quality of life improved in responders. The remarkably low levels of endogenous EPO in our patients with squamous cell carcinoma, most of whom had been treated with cisplatin-or carbo-platin-containing regimens, suggest that anemia in these cases had been at least partly chemotherapy induced. In myeloma patients, the blunted EPO response to the anemic condition may have been partly caused by subclinical tubular insufficiency induced by toxic paraproteins. Future studies should aim to elucidate factors which are responsible for the inability of some patients to respond to rHuEPO treatment, even though in multiple myeloma and squamous cell carcinoma these non-responders are a small minority.