The in vivo response to recombinant human granulocyte-monocyte colony-stimulating factor (rHu GM-CSF) in facilitating the reconstitution of granulomonopoiesis was evaluated in a patient with Graves' disease who developed severe aplastic anemia during methimazole therapy. After 10 days of treatment with rHu GM-CSF, the neutrophil and monocyte counts rose to 1.65 x 10(9)/l and 0.41 x 10(9)/l, respectively. However, the patient was still dependent on erythrocyte and platelet transfusions. Two days after rHu GM-CSF withdrawal, the neutrophil count dropped off to 0.41 x 10(9)/l.rHu GM-CSF was reinitiated for 2 days along with glucocorticosteroids. With this combined therapeutic approach, the neutrophil count returned to normal and remained stable, and both Hb and platelet values began to improve. It is concluded that the combination of rHu GM-CSF and glucocorticosteroids can be used as a therapeutic option that may lead to beneficial results in drug-induced aplastic anemia.