In a dose titration study we tested the efficacy and tolerance of recombinant human erythropoietin (rhEPO) in 10 patients with myelodysplasia (MDS) and 2 patients with idiopathic myelofibrosis. Patients with a haemoglobin level < 100 g/l were treated as out-patients for 12 weeks with daily doses ranging from 30 U/kg body weight (BW) up to 240 U/kg BW in non-responders. Of the 10 patients with MDS, 6 were suffering from refractory anaemia with side-roblasts (RAS) and 4 from refractory anaemia with an excess of blasts. The median age was 73 years (range 41-81). Two patients with RAS responded with a rise in haemoglobin concentration to& < 130 g/l. They had not been transfusion-dependent prior to treatment. Both patients had relatively low serum concentrations of immunoreactive EPO. There was neither a rise in haemoglobin nor a reduction in transfusion dependence in any of the other patients. It may be concluded that rhEPO is possibly effective in a subgroup of MDS patients where the disease is less advanced. None of the transfusion-dependent patients benefited.