A clinical trial of recombinant human granulocyte colony-stimulating factor (rG-CSF), produced by Chinese hamster ovary cells, was conducted in 66 patients receiving intensive chemotherapy for non-Hodgkin's lymphoma. Each patient received 2 cycles of CHOP therapy, and one cycle of them was performed with rG-CSF treatment and another one without rG-CSF treatment, in a cross-over fashion. rG-CSF (0.4, 2, 5, 10 micrograms/kg/day) was given intravenously or subcutaneously to each patient for 14 days from 2 days after initiation of the chemotherapy. rG-CSF increased the absolute neutrophil counts (ANC) at nadir, and reduced the period of neutropenia with ANC less than 1,000/mm3 and also the period for restoration to ANC greater than or equal to 2,000/mm3 after initiation of chemotherapy. These effects were remarkable at doses of more than 5 micrograms/kg/day intravenously and 2 micrograms/kg/day subcutaneously. Fourteen infective episodes were observed during the cycles of chemotherapy without rG-CSF treatment, while 7 infective episodes were observed during the cycles with rG-CSF treatment. rG-CSF was well tolerated. These results demonstrated that rG-CSF was effective in neutropenia induced by cancer chemotherapy at a intravenous dose of 5 micrograms/kg/day and a subcutaneous does of 2 micrograms/kg/day.