The quinolones differ in their mechanisms of bacterial killing. The rate of bacterial killing by quinolones can be influenced by the addition of bacterial protein or RNA synthesis inhibitors, and the growth phase of the bacterium. In this study, we compared the killing activities of gatifloxacin, trovafloxacin, ciprofloxacin and norfloxacin against staphylococci, pneumococci and Escherichia coli. Gatifloxacin killing of these organisms occurred regardless of the metabolic state of the microbes. Unlike the comparator quinolones, gatifloxacin killing was not influenced by the addition of bacterial protein or RNA synthesis inhibitors. Gatifloxacin was able to kill non-dividing staphylococcal and E. coli cells.