Granulocyte colony-stimulating factor (G-CSF) is believed to be useful for shortening the duration of granulocytopenia and for minimizing the decrease in the granulocyte count caused by chemotherapy for non-Hodgkin's lymphoma. In the present study we investigated the effect of G-CSF on bone marrow suppression caused by chemotherapy for non-Hodgkin's lymphoma of the head and neck. The leukocyte and neutrophil nadirs were significantly higher, while the duration of leukopenia, the time to recovery, and the time to the nadir were significantly shorter when G-CSF was administered prophylactically from 48 h after the completion of chemotherapy than when it was administered after the leukocyte and neutrophil counts had reached nadir. G-CSF had no influence on other blood cell components and caused no severe adverse events.