Currently, 2 granulocyte colony-stimulating factors are available in the United States--filgrastim and pegfilgrastim. In patients receiving chemotherapy for solid tumors, lymphoma, and acute myelogenous leukemia, these agents reduce the duration of severe neutropenia, decrease the incidence of febrile neutropenia, and facilitate on-time delivery of scheduled doses of chemotherapy. In addition, substantial data document the benefits of using these agents in patients undergoing peripheral blood progenitor cell mobilization and in patients who have undergone bone marrow transplantation or peripheral blood progenitor cell transplantation. Recent studies suggest that for all of these indications, the efficacy of pegfilgrastim, the newest agent, is comparable to or greater than that of filgrastim. Like filgrastim, pegfilgrastim is generally well tolerated. An important advantage of pegfilgrastim, however, is its once-per-cycle schedule of administration. Patients and health care providers are likely to prefer the administration schedule of pegfilgrastim to the daily administration schedule required with the use of filgrastim. Furthermore, the more convenient schedule of pegfilgrastim may be associated with greater treatment adherence and increased patient quality of life.