The activity of ciprofloxacin, sparfloxacin and moxifloxacin was determined for 205 Enterococcus faecalis isolates from patients of five hospitals (Warsaw, Poland; collected from 2000 to 2002). Ciprofloxacin resistant and intermediate isolates were numerous (53.7%). Among them, highly resistant (MIC > or = 16 mg/l) isolates predominated (98%). Isolates resistant to ciprofloxacin were also resistant to sparfloxacin and moxifloxacin. The parC and gyrA QRDRs (quinolone-resistance-determining region) of 11 isolates with ciprofloxacin MICs from 1 to 256 mg/l were analysed by DNA sequencing. In ParC one kind of amino acid substitution (of Ser-85 to Ile) in 9 E. faecalis strains with MICs from 16 to 256 mg/l was observed. In GyrA Ser-84 was changed to one of four different amino acids: Arg, Ile, Cys or Tyr, however no association between the amino acid type and MIC value was found. The last two substitutions have not been reported to date for E. faecalis. Moreover, our results may suggest that mutations within parC and gyrA are associated with development of a high-level of ciprofloxacin resistance.