Recombinant human granulocyte colony-stimulating factor (rhG-CSF) and erythropoietin (rhEPO) were used to treat patients with aplastic anemia (AA). In terms of effects on erythrocyte recovery, the combined use of rhG-CSF and rhEPO showed a favorable response in 6 of 14 (42.9%) patients with moderate AA following 10 weeks treatment and in 3 of 14 (21.4%) patients thereafter. However, the response was poor in patients with severe AA (3/13). A favorable response in severe AA was observed in 1 of 13 (7.7%) patients following 10 weeks treatment and in 2 of 13 (15.4%) patients thereafter. The overall effect on erythrocytes was observed in 44.4% patients. A dose of 400 micrograms/m2 G-CSF was sufficient to cause an increase in neutrophil count and 100 IU/kg rhEPO appeared to be sufficient to cause an increase in erythrocyte count. In 6 of 27 (22.2%) patients, a trilineage response was observed. Interestingly, a delayed and long-lasting effect was obtained in 5 of 27 (18.5%) patients. These results suggest that rhG-CSF can synergize with rhEPO in erythrocyte response, especially in patients with moderate AA.