INTRODUCTION: Recombinant granulocyte colony-stimulating factor (G-CSF) may aid engraftment post high-dose chemo-/radiotherapy in patients with haematological malignancies undergoing allogeneic bone marrow transplantation (BMT); however, the effects of G-CSF on graft-versus-host disease (GvHD), relapse, and survival are not well defined. METHODS: In this double-blind, randomized, placebo-controlled, multicentre, phase 3 study, the effects of the G-CSF Filgrastim on neutrophil and platelet recovery, and on clinical outcomes were evaluated. Patients (12-55 years) receiving an allogeneic BMT for a haematological malignancy were randomized to receive Filgrastim 5 microg/kg or placebo. Study treatment was continued until patients achieved an absolute neutrophil count (ANC) >/=0.5 x 10(9)/L, or until day 42. RESULTS: Fifty-one patients (Filgrastim, N = 25; placebo, N = 26) were evaluable. Patients treated with Filgrastim had significantly faster engraftment with ANC >/=0.5 x 10(9)/L being achieved after a median (range) of 15.0 (1.0-22.0) days vs. 19.0 (15.0-28.0) days for placebo (P< 0.0001). The incidence of GvHD was comparable for both groups. During the limited follow-up (2 years), Filgrastim had no adverse effect on mortality and possibly reduced the rate of relapse.