We undertook a comparative study of Pegfilgrastim vs. Filgrastim after high-dose melphalan and autologous peripheral blood stem cell transplantation (APBSCT) in multiple myeloma (MM) patients. Thirty-seven consecutive patients were randomly assigned to receive a single 6 mg dose of Pegfilgrastim on day 1 post-transplant (n = 18 patients) vs. daily subcutaneous injections of Filgrastim 5 microg/kg (n = 19 patients) starting on day 5 post-transplant. The median duration of grade 4 neutropenia in the Pegfilgrastim and Filgrastim groups was 5 and 6 d, respectively (P = ns). The results for the two groups were also not significantly different for time to neutrophil and platelet recovery, but incidence of febrile neutropenia (61.1% vs. 100%, P = 0.003) and duration of febrile neutropenia (1.5 d vs. 4 d, P = 0.005), were lower in the Pegfilgrastim arm. After initial haematopoietic reconstitution, we observed significantly higher value of leukocytes x 10(9) L on day 15 (6.0 vs. 2.7, P = 0.004), in the Pegfilgrastim group compared with the Filgrastim group. This study shows that a single injection Pegfilgrastim can be used with safety and efficacy similar to those provided by daily injections of Filgrastim and it is associated with a decrease incidence of infectious events after APBSCT in MM patients.