It is known that Granulocyte colony-stimulating factor (G-CSF) accelerates neutrophil recovery following bone marrow transplantation (BMT), though the optimal timing is not clear. We have undertaken a pilot study in 19 recipients of autologous BMT for non-myeloid malignancy, in which G-CSF was commenced 10 (13 cases) or 7 (6 cases) days after BM infusion. These patients were compared with 18 historical controls, who did not receive G-CSF. The median time to achieve both 0.5 and 1.0 x 10(9) neutrophils/Litre was significantly shorter in the treated group (18 and 21 days respectively) than the control group (20.5 and 29 days; p = 0.03 and 0.02 respectively). No differences between the two groups were seen for the number of febrile days, days on antibiotics or the cost of the antibiotics. G-CSF-treated patients remained in hospital for significantly less time after marrow infusion (21 days compared to 29 days; p = 0.007). The cost of the G-CSF therapy was offset by the decreased bed utilisation, so that the median combined antibiotic, G-CSF and hospitalisation cost was 754 pounds less for G-CSF treated patients. It is concluded that delaying the commencement of G-CSF after autologous BMT accelerates neutrophil recovery, and may allow earlier discharge from hospital, whilst not adversely affecting the cost of the procedure.