G-CSF (5 mg/kg/day Filgrastim) was administered from day 7 after autologous bone marrow transplantation (ABMT) in a series of 17 patients treated for multiple myeloma or non-Hodgkin's lymphoma. In comparison with retrospective controls receiving ABMT without G-CSF and matched for age, underlying disease, disease status at ABMT, number of CFU-GM/kg reinfused, conditioning regimen and number and type of chemotherapy courses prior to ABMT, the duration of neutropenia, intravenous antibiotics and hospitalization was significantly reduced in the G-CSF group (p < 0.001). Delaying the administration of G-CSF after ABMT is an interesting possibility which merits further exploration in prospective randomized studies.