Methicillin-resistant Staphylococcus aureus (MRSA) is a common nosocomial pathogen ac-counting for 5 to 24% pf all staphylococci isolated in Hua Shan Hospital. It has recently emerged as a major clinical and epidemiological problem. Most strains of Mrsa are resistant to all commonly used antimicrobial agents except vancomycin. Some newer quinolones demonstrate good antibacterial activity against MRSA, and have been used in the treatment of MRSA infections. However, it has been reported that resistance may rapidly develop. In this study, MIC values for 101 clinical strains of MRSA were determined by the agar dilution method, by use of Mueller-Hinton agar with an in-oculum of 105 cfu/spot. From 1985 to 1987 the rates of inhibition with norfloxacin, ofloxacin and ciprofloxacin at a concentration of 2 mg/L against MRSA were 80, 88 and 88%, respectively, much higher than in 1991 when rates had decreased to 9.8%, 19.6% and 19.6, respectively