Filgrastim (granulocyte colony stimulating factor) recently became commercially available for the treatment of chemotherapy-induced neutropenia. Studies have shown that filgrastim induces a dose-dependent granulocytosis in humans, thereby shortening the period of neutropenia in patients treated conventionally with submarrow ablative doses of chemotherapy, as well as with marrow ablative therapy given in the bone marrow transplant setting. By reducing the incidence and severity of infections and mucositis in patients treated with chemotherapy, it has a significant economic impact since it shortens the duration of antibiotic administration and hospitalization. Adverse reactions reported are limited to mild to moderate bone pain. Several other potential applications are being investigated for filgrastim, including treatment of patients with myelodysplastic syndrome and congenital neutropenia.