It is well established that recombinant human G-CSF accelerates neutrophil recovery following autologous peripheral blood stem cell transplantation (PBSCT). However, the optimal timing of G-CSF following transplantation remains unknown. We have conducted a retrospective analysis of patients treated with either early, day +1 (n = 42) or delayed, day +4 (n = 39) administration of G-CSF following autologous PBSCT for a variety of hematologic malignancies and solid tumors. G-CSF was given at a dose of 5 microg/kg/day i.v. as a 2 h infusion beginning either day +1 or day +4 following PBSC infusion and continued until the total white blood count (WBC) was >10 x 10(9)/l. The numbers of transplanted CD34+ cells were similar in each group. Treatment with early administration of G-CSF resulted in a significantly shorter time to an absolute neutrophil count (ANC) of >0.5 x 10(9)/l (8.5 vs 10.0 days, P < 0.0003) and shorter length of hospitalization (16.3 vs 18.6 days, P < 0.0008), a trend towards a reduced incidence of infection (53 vs 72%) and a significant decrease in the duration of non-prophylactic antibiotic (NPA) therapy for neutropenic fever (4.0 vs 7.5 days, P < 0.009) compared to day +4 administration. Despite the additional cost of G-CSF, the reduction in the hospitalization and NPA therapy with early G-CSF administration resulted in 11% cost savings overall per transplant at our institution.