Arbekacin (ABK) was administered to 17 patients with MRSA infections that complicated underlying hematopoietic disorders, and the efficacy and safety were evaluated. The underlying diseases included acute myelocytic leukemia (8 cases), acute lymphocytic leukemia (1) myelodysplastic syndrome (3), chronic myelocytic leukemia (1), non-Hodgkin's lymphoma (2), Hodgkin's disease (1) and adult T cell leukemia (1). The infections consisted of septicemia (5 cases), pneumonia (4), upper respiratory tract infections (6) and urinary tract infections (2). ABK was administered by i.v. drip infusion in daily doses of 150-200 mg, given in two divided dosages. The therapeutic efficacies were: excellent in 2 (2 septicemias), good in 7 (1 septicemia, 4 upper respiratory infections, 2 urinary tract infections), fair in 2 (septicemia and pneumonia) and poor in 6 (1 septicemia, 3 pneumonias, 2 upper respiratory infections). As a side effect, reversible renal dysfunction was detected in four cases. Causative bacteria were isolated from six cases. They were all coagulase type II and MIC's of ABK were from 0.25 microgram/ml to 4.0 micrograms/ml. Arbekacin therapy was found to be effective even in patients with hematopoietic disorders accompanied by MRSA infections.