Recombinant granulocyte colony-stimulating factor (rhG-CSF) has been shown to hasten granulocyte recovery after autologous BMT. In current protocols, rhG-CSF treatment starts 1 day after BM reinfusion. Our study retrospectively examined the effects on haematological recovery of a day 6 delayed administration. Seventy-eight patients receiving autologous BMT for malignant lymphoma (21 non-Hodgkin's lymphoma and 9 Hodgkin's disease) or solid tumors (33 breast carcinoma and 5 ovarian carcinoma) were split up into three study groups. Two groups receiving a 5 micrograms/kg/day of rhG-CSF starting either 1 day (day +1 group, n = 25 patients) or 6 days (day +6 group, n = 24 patients) after BM reinfusion were compared with 29 historical control patients. Granulocyte recovery to 0.5 x 10(9)/l was 12 days in day +6 and day +1 groups versus 16 days in control group (p < 0.005) without any difference in other hematological parameters, infectious complications or length of hospitalisation between the three groups. The day +6 administration allows elimination of a median of 7 days rhG-CSF. It has been concluded that the day +6 administration gives the same clinical benefit as day +1 administration with consequent cost reductions.