Ciprofloxacin has been extensively investigated in various animal models of infection. These studies have demonstrated ciprofloxacin to possess in-vivo activity comparable to its activity previously demonstrated in vitro. The reported investigations have shown ciprofloxacin to be equal or superior to all other agents tested for Gram-negative, as well as most Gram-positive bacteria. These studies have also demonstrated that in-vitro susceptibility testing correlates well with in-vivo therapeutic outcome, in the animal models. The reported information has provided new directions for use of this agent, including the possibility for the use of ciprofloxacin as a replacement for aminoglycosides in combination therapy of serious enterococcal infections.