Granulocyte-macrophage colony stimulating factor (GM-CSF) has been tested for tolerability and efficacy on a compassionate need case basis in 17 patients (5 females, 12 males aged 4-72 years, median 35 years). GM-CSF was given at the rate of 3.5-32 micrograms/kg for 2-64 days as a continuous infusion for the following indications: impending rejection following bone marrow transplantation (5 patients), severe neutropenia secondary to chemotherapy in tumor patients (5), severe aplastic anemia (3), immune granulocytopenia (2) and accidental overdose with cytostatic agents (2 patients). Tolerance of GM-CSF was good in regard to doses of up to 16 micrograms/kg. Fever, myalgia and eosinophilia were the most frequent side effects. The patient treated with 32 micrograms/kg developed thrombosis of the vena cava. Efficacy is more difficult to assess in this heterogenous population, but 11 of 17 patients showed increased granulocyte counts and 3 patients clearly recovered from severe neutropenia. The role of GM-CSF in this recovery, however, cannot be proven. The results further indicate that GM-CSF cannot reverse ongoing rejection following allogenic BMT and cannot correct immune neutropenia. The value of GM-CSF therapy in patients with severe aplastic anemia and in the context of chemotherapy still needs to be defined. It is certainly indicated in patients with an accidental overdose of chemotherapeutic agents.