We evaluated the efficacy of combined therapy of arbekacin (ABK) and imipenem/cilastatin (IPM/CS) against infections by methicillin-resistant Staphylococcus aureus (MRSA). The MICs of ampicillin, cefmetazole, cefotiam, cefuzonam, flomoxef, fosfomycin, ofloxacin, minocycline, ABK and IPM/CS against clinically isolated strains of MRSA were examined. Almost all strains of MRSA were resistant to these antibiotics except ABK. Furthermore, combination of ABK and IPM/CS showed smaller MICs than that of ABK or IPM/CS alone. All fractional inhibitory concentration indices (FIC indices) of ABK plus IPM/CS were lower than 0.75. The efficacy rate of combined therapy of ABK and IPM/CS in 22 patients with MRSA infections (15 patients with pneumonia, 3 patients with chronic bronchitis, 2 patients with sepsis, a patient with subcutaneous abscess and a patient with DPB) was 68%. And no patients had adverse reactions. Six (27%) of 22 strains of MRSA were eradicated. Significant correlations were found between bacteriological effect and severity of disease, and between serum albumin level and clinical effect.