Darbepoetin-alpha, a novel hyperglycosylated erythropoiesis-stimulating protein, was administered to 20 patients with myelofibrosis with myeloid metaplasia and anaemia. The initial weekly dose, 150 mug, was increased to 300 mug when no response was observed after 4-8 weeks. Eight patients (40%) responded to treatment, including six complete and two partial responses, and five maintained their response at a median follow-up of 12 months (range 4-22). Univariate analysis indicated that older age was the only factor associated with a favourable response to treatment (P = 0.006). None of the patients with appropriate serum erythropoietin levels responded. Treatment was usually well tolerated.