We have used recombinant human (rh) GM-CSF in two 12-year-old Fanconi's aplastic anaemia patients. They had not received any previous therapy except blood transfusions. Each patient was given three 21 d courses of rh-GM-CSF, the first two at a dose of 3.5 micrograms/kg/d and the third at 7 micrograms/kg/d s.c. There were significant increases in WBC and absolute neutrophil counts after the first week of rh-GM-CSF which lasted as long as the treatment was continued. Following the cessation of treatment, WBC and ANC dropped rapidly. We conclude that rh-GM-CSF can be used in FAA, especially in severely neutropenic cases.