Neutropenia is the most important dose-limiting toxicity of myelotoxic chemotherapy. Current guidelines recommend primary prophylactic use of granulocyte colony stimulating factor (G-CSF) with chemotherapy regimens associated with an incidence of febrile neutropenia (FN) of at least 40% and in patients at high risk of infections, such as the elderly. Using prophylactic G-CSF support, planned chemotherapy doses are administered on time more frequently. Pegfilgrastim is a rationally designed recombinant human G-CSF with a sustained duration of action. A once-per-cycle 6-mg fixed dose of pegfilgrastim reduced the duration of severe neutropenia and the incidence of FN as efficiently as daily filgrastim in standard or dose-dense chemotherapy regimens in young and elderly patients with breast cancer, non-small-cell lung cancer and lymphomas. The safety profile of onceper- cycle pegfilgrastim is comparable with that of daily filgrastim. In conclusion, a fixed-dose of pegfilgrastim given once per cycle is a suitable substitute for body weight-based daily dosing of G-CSF, an improvement which should be particularly beneficial for outpatients receiving myelotoxic chemotherapy.