Previously untreated patients who had anemia (hemoglobin level, less than or equal to 10 g/dL) caused by myelofibrosis (MF) (16 patients) or other myeloproliferative disorders (13 patients) were given the opportunity to participate in a prospective randomized study-to be treated either with 30 mg/day of oral fluoxymesterone and necessary transfusions or by transfusions alone. Of the 24 patients whose data could be evaluated, four (29%) of 14 responded well to fluoxymesterone therapy (hemoglobin level rise, of greater than 2 to greater than 10 g/dL and relief of symptoms of anemia), whereas, in the transfusion arm, there were no good "responders"; one of ten patients was a partial "remitter" (responder), with a rise in the hemoglobin level of 1 to 2 g/dL. All responders to fluoxymesterone therapy showed a 50% or more maximum uptake of injected ferrous citrate Fe 59 into RBC hemoglobin, whereas no nonresponder met this criterion. All responders had MF (marrow more than one third replaced by collagen). There was no significant difference in survival of patients in the two arms of the study.