Two cases of endocarditis, one caused by high-level gentamicin-resistant Enterococcus durans and the other by high-level gentamicin- and glycopeptide-resistant Enterococcus faecalis. successfully treated with a combination of ampicillin and a fluoroquinolone are reported. Both strains were susceptible to ampicillin. Enterococcus faecalis was susceptible to ciprofloxacin and to ofloxacin, but Enterococcus durans was moderately resistant to these agents. Microbiological and clinical cure was obtained with a 6-week course of ampicillin plus ciprofloxacin in one case and with ofloxacin in the second case due to intolerance to ciprofloxacin. The efficacy of the treatment was predicted in vitro by time-kill studies and by adequate serum bactericidal titres.