Arbekacin has excellent antibacterial activity and is also effective against methicillin-resistant Staphylococcus aureus (MRSA) resistant to aminoglycosides such as gentamicin, tobramycin, and methicillin-susceptible Staphylococcus aureus (MSSA). By coagulase typing, four different coagulase types were identified from 358 strains out of 387 MRSA isolated during 1993 in Japan. Among isolates collected in the survey period, about 89% had type 2 coagulase, and only a few had type 3 (4.5%), 4 (2.5%) or 7 (3.6%) coagulase. The distribution of coagulase types in Japan is quite different from those outside Japan which had type 4 coagulase. More than 72% of strains with types 2, 7 and untyped coagulase had high resistance to methicillin. All of the isolates with types 2, 3, 4, and 7 coagulase were highly resistant to gentamicin and tobramycin. 89% of isolates with type 7 coagulase, 2.5% of those with type 2 coagulase and 6.3% of those with type 3 coagulase were found to be arbekacin-resistant. No arbekacin-resistant MRSA was detected among the isolates with type 4 coagulase. In the present study, the authors attempted to determine the strong antibiotic activity of arbekacin against MRSA and particularly gentamicin-resistant MRSA. Arbekacin is not modified by the aminoglycoside-modifying enzyme, ANT (4')-1. Although arbekacin is inactivated by the enzyme APH (2")/AAC (6') which can modify both gentamicin and tobramycin, the rate of modification of arbekacin by this enzyme is only 17% or less of that of gentamicin.