The purpose of the study was to evaluate the effect of delayed granulocyte colony-stimulating factor (G-CSF) use on hematopoietic recovery post-autologous peripheral blood progenitor cell (PBPC) transplantation. Patients were randomized to begin G-CSF on day +1 or day +7 post transplantation. Thirty-seven patients with lymphoma or myeloma undergoing high-dose therapy and autologous PBPC rescue were randomized to daily subcutaneous G-CSF beginning on day +1 or day +7 post-transplant. Patients < or =70 kg received 300 microg/day and >70 kg 480 microg/day. All patients were reinfused with PBPCs with a CD34+ cell count >2.0 x 10(6)/kg. Baseline characteristics of age, sex and CD34+ cell count were similar between the two arms, the median CD34+ cell count being 5.87 x 10(6)/kg in the day +1 group and 7.70 x 10(6)/kg in the day +7 group (P=0.7). The median time to reach a neutrophil count of >0.5 x 10(9)/l was 9 days in the day +1 arm and 10 days in the day +7 arm, a difference which was not statistically significant (P=0.68). Similarly, there was no difference in median days to platelet recovery >20000 x 10(9)/l, which was 10 days in the day +1 arm and 11 days in the day +7 arm (P=0.83). There was also no significant difference in the median duration of febrile neutropenia (4 vs 6 days; P=0.7), intravenous antibiotic use (7 vs 8 days; P=0.54) or median number of red blood cell transfusions (4 vs 7 units; P=0.82) between the two arms. Median length of hospital stay was 11 days post-PBPC reinfusion in both groups. The median number of G-CSF injections used was 8 in the day +1 group and 3 in the day +7 group (P < 0.0001). There is no significant difference in time to neutrophil or platelet recovery when G-CSF is initiated on day +7 compared to day +1 post-autologous PBPC transplantation. There is also no difference in number of febrile neutropenic or antibiotic days, number of red blood cell transfusions or length of hospital stay. The number of doses of G-CSF used per transplant is significantly reduced with delayed initiation, resulting in a significant reduction in drug costs. For patients with an adequately mobilized PBPC graft, the initiation of G-CSF can be delayed until day +7 post-PBPC reinfusion.