Human recombinant granulocyte-macrophage colony-stimulating-factor has been employed, on a compassionate basis, in 14 hematological patients in order to reduce the duration of the neutropenic period after high-dose chemotherapy for the treatment of hematological malignancies (7 traditional CHT courses, 7 autologous bone marrow transplantations). The compound was administered intravenously by 6-hour infusion at a dose of 5 microgram/kg/day until the patient reached at least 1000 PMN in the peripheral blood. Eleven out of the 13 evaluable patients showed a significative improvement in hemopoietic recovery, even though in CHT patients hematological reconstitution was higher in terms of PMN counts. The ABMT patients, however, showed a faster myeloid recovery than that obtained both in a group of 14 NHL and in a series of 8 MM previously submitted to ABMT in our Institution. Moreover the increase in peripheral neutrophils appeared to be stable, since it was maintained throughout one month after the end of rhGM-CSF therapy. We did not observe effects on platelet or erythrocyte recovery. We conclude that rhGM-CSF is active in accelerating the recovery of myelopoiesis, without significant toxic or collateral effects.