The effects of sarafloxacin, a newly developed veterinary fluoroquinolone antimicrobial, on 15 strains of aerobic and anaerobic bacteria of human origin were assessed under simulated human gut conditions. An in vitro gut simulation model was designed to mimic the situation of sarafloxacin (free and bound to meat) passing through the human gastrointestinal tract. The survival of bacteria in the simulation model and any subsequent change in the sensitivity of isolates to sarafloxacin were measured. The inhibitory level of sarafloxacin for the tested bacteria was strain dependent. It appeared that in broth culture Escherichia coli isolates were sensitive to sarafloxacin concentrations 5-fold lower than the concentrations present in the simulated gut model, suggesting that sarafloxacin may be partially unavailable due to absorption to organic matter in the model. There was no significant observed change in the sarafloxacin sensitivity of the bacterial strains exposed to the compound in the model.