Modern chemotherapy programmes render patients susceptible to bacterial and fungal infections, and the risk of developing febrile neutropenia after a chemotherapy course is in proportion to the severity and duration of the neutropenia thus caused. This double-blind randomized study presents details of 29 patients who developed febrile neutropenia an average of 10 days after their course of chemotherapy for different types and stages of malignancy. Fourteen received granulocyte/macrophage colony stimulating factor (GM-CSF) and 15 placebo during 7 consecutive days as subcutaneous injections. The GM-CSF group demonstrated significant increases in total white blood cell count (TWBC) and absolute neutrophil count (ANC) from the morning of the third day of the study. The study concludes that GM-CSF has an important therapeutic role in the treatment of febrile neutropenia that arises during intensive chemotherapy programmes but further studies of dosage and therapy duration are required, as is the development of methods of assessing bone marrow vitality.