A seven-year-old girl with transient leukopenia and erythroblastopenia which developed after the administration of acyclovir is presented. Acyclovir infusion was given in a dose of 5 mg/kg/every eight hours. On the third day of therapy the hemoglobin level fell to 9.9 g/dl, the hematocrit was 26%, the white blood cell count 4000 percent/mm3, red blood cells 3.2 million percent/mm3. Bone marrow aspiration showed a decrease in the number of erythoblasts and a relative increase in the number of promyelocytes and myelocytes. Therapy was discontinued on the fifth day, and on the seventh day the findings were normal including the bone marrow aspiration. We could not find any other reason which would cause transient erythroblastopenia and leukopenia in our patient.