A phase II dose-escalation trial was conducted to ascertain low-dose thalidomide safety and response in patients with advanced myelofibrosis with myeloid metaplasia (MMM). Thalidomide was administered together with current therapy to 63 patients, starting at 50 mg daily and increasing to 400 mg as tolerated. Half of the patients sustained daily doses more than 100 mg and the drop-out rate was 51% at 6 months: the drop-out rate was lower in patients with high baseline fatigue score. At efficacy analysis, anemia was ameliorated in 22% of the patients and transfusions were eliminated in 39% of transfusion-dependent patients. Platelet count increased by 50 x 10(9)/L or more in 22% of patients with an initial count lower than 100 x 10(9)/L. Splenomegaly decreased by more than 50% of the initial size in 19% of patients. Reduction of an overall disease severity score occurred in 31% of patients and was associated with a significant reduction of fatigue. Disease severity amelioration was independently predicted by a high baseline myeloproliferative index (ie, large splenomegaly, thrombocytosis, or leukocytosis). Low-dose thalidomide displays an acceptable toxicity profile and provides an objective and subjective advantage to a relevant portion of MMM patients.