The suppression of faecal Escherichia coli by quinolones was studied in a randomized cross-over phase I trial with single oral doses of 400 mg rufloxacin or norfloxacin. Both drugs caused > 70% decontamination in a similar number of subjects in the 72 h post-dose period (83% vs 100% respectively), but suppression of E. coli at 168 h was significantly (P < 0.05) higher after rufloxacin (83.3 vs 40%).