The fluoroquinolones are used in the treatment of a variety of bacterial infections. These agents inhibit the DNA gyrase, abolishing its activity by interfering with the DNA rejoining reaction. The inhibition of the resealing leads to the liberation of fragments that are subsequently destroyed by the bacterial exonucleases. All fluoroquinolones accumulate within bacteria very rapidly, so that a steady-state intra bacterial concentration is obtained within a few minutes. Resistance develops slowly and is usually chromosomal and not plasmid mediated. However, development of resistance and transfer between animal and human pathogens has become a fervently argued issue among the microbiologists. Another concern regarding the use of new quinolones in the veterinary field is a possible detrimental effect on the environment. It still seems unlikely that the controlled use of veterinary quinolones will give rise to unfavourable effects on the environment.