A combination of ciprofloxacin and fosfomycin was evaluated for synergism employing time-kill experiments. A total of 59 clinical isolates of gram-negative bacteria was examined. All organisms were moderately sensitive or resistant to ciprofloxacin; 72.9% also showed moderate sensitivity or resistance to fosfomycin. After 24 h, synergism was seen in 22% of the strains, i.e. less than reported by other authors. There was no correlation between synergistic action and sensitivity to ciprofloxacin and fosfomycin, respectively.