The purpose of this study was to compare the efficacy and safety of a single subcutaneous injection of pegylated filgrastim with daily filgrastim as a prophylaxis for neutropenia induced by commonly used chemotherapy regimens. Fifteen centers enrolled 337 chemotherapy-naive cancer patients with normal bone marrow function. All patients randomized into AOB and BOA arms received two cycles of chemotherapy. Patients received a single dose of pegylated filgrastim 100 µg/kg in cycle 1 (AOB) or cycle 2 (BOA) and daily doses of filgrastim 5 µg/kg/day in cycle 1 (BOA) or cycle 2 (AOB). Efficacy and safety parameters were recorded. The primary end point was the rate of protection against grade 4 neutropenia after chemotherapy [defined as the rate at which the absolute neutrophil count (ANC) remained >0.5×10(9)/l throughout the entire cycle]. Ninety-four percent of patients receiving pegylated filgrastim or filgrastim did not develop grade 4 neutropenia. The incidence of ANC<1.0×10(9)/l was 16.0% (50/313) after support with either pegylated filgrastim or filgrastim. The incidences of febrile neutropenia and antibiotic administration were similar in both groups. Notably, faster ANC recovery was observed with pegylated filgrastim support. The ANC nadir was also earlier with pegylated filgrastim (day 7) support than with filgrastim support (day 9), although the depth of nadir was not significantly different. A single subcutaneous injection of pegylated filgrastim 100 μg/kg provided adequate and safe neutrophil support comparable with daily subcutaneous injections of unmodified filgrastim 5 μg/kg/day in patients receiving commonly used standard-dose mild-to-moderate myelosuppressive chemotherapy regimens.