The efficacy of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) in graft failure after bone marrow transplantation (BMT) has been evaluated in 25 patients. rhGM-CSF was administered intravenously at a dose of 5 or 10 micrograms/kg. Fourteen patients (seven allogeneic BMT [allo-BMT], seven autologous BMT [ABMT]) were treated for primary bone marrow failure (no granulocyte recovery after BMT), and 11 cases (all allo-BMT) received rhGM-CSF for secondary bone marrow failure (absolute neutrophil count lower than 0.5 x 10(9)/L after a previously sustained granulocyte recovery). Two allo-BMT and three ABMT patients with primary bone marrow failure achieved a granulocyte response to rhGM-CSF. In contrast, nine patients with primary graft failure did not respond to rhGM-CSF (four ABMT, three HLA-identical T-depleted BMT, one minor mismatch BMT, one unrelated BMT). Ten of 11 allo-BMT patients treated for secondary bone marrow failure attained an ANC higher than 0.5 x 10(9)/L, but most became severely neutropenic again at a median time of 4 weeks. The possible cause triggering graft failure (graft-vs.-host disease [GVHD], cytomegalovirus [CMV] infection) remained unsolved in most of these cases. Actuarial probability of survival of the entire series was 16 +/- 9% at 15 months. The severity of graft failure and the presence of other concomitant complications in most of our patients may justify these poor results. In conclusion, rhGM-CSF had less efficacy in patients with primary bone marrow failure than in those with secondary bone marrow failure. In the latter setting, measures addressed to correct the initial cause of graft failure are mandatory.