The purpose of this study was to develop a cost-effective protocol for the mobilization of peripheral blood stem cells (PBSC) in patients with malignancy. Thirty consecutive patients were randomized to mobilize PBSC with the late addition of a standard 250 microg dose of G-CSF (Neutrogen) from day 8 or early addition of the same dose of G-CSF from day 2, following cyclophosphamide (CY) 4 g/m2. The median yield of CD34+ cells from evaluated patients was 7.87 x 10(6)/kg (range, 2.06-27.25), collected in a median of four apheresis (range, 2-9). Target CD34 + cell doses > or = 2.0 x 10(6)/kg were achieved in all patients able to be evaluated. There were no statistically significant differences in CD34+ cell yields or toxicities. Overall engraftment occurred with median days to neutrophils > or = 0.5 x 10(9)/L or platelets > 20 x 10(9)/L of 11 and 17 days, respectively. However, the duration of G-CSF administration was markedly shorter in the late use of G-CSF group than in the early use of G-CSF group, with a median of 9 days compared with 15 days (p<0.001). PBSC harvesting after priming with CY plus delayed use of G-CSF made it a safe and cost-effective procedure.