Killing kinetic experiments were performed with moxifloxacin, a novel fluoroquinolone, vancomycin, clarithromycin, cotrimoxazole, gentamicin, rifampicin and with moxifloxacin in combination with each of the above drugs against six methicillin-resistant Staphylococcus aureus clinical isolates. Half of the strains were ciprofloxacin-resistant. The early bactericidal effect of moxifloxacin alone was substantially greater than that of the other tested drugs. No antagonism was observed between moxifloxacin and each of the other drugs. For each combination the mean decrease in the number of organisms (after 6 hours) was comparable to that achieved with moxifloxacin alone, however, when moxifloxacin was tested with gentamicin, a slight increase in the bactericidal effect was observed.