In this study, the effects of enrofloxacin (10 mg/kg. b. w.) givenin the drinking water for 3 successive days on the immune response ofnon-vaccinated and vaccinated chickens with NDV vaccine werestudied. The obtained results revealed the following.1- Effect on the cellular immune response:A - Totalleukocytic count:The total leukocytic count was not significantly affected duringthe course of the experiment (5 weeks) .The lymphocyte stimulation index was significantly depressedstarting from 3rd day up to the 4t h week post treatment in thenonvaccinated chicken in the presence of the nonspecific mitogenConcanavalin- A, Poke weed , phytohaemagglutinin and the specificantigen NDV vaccine. The same effect started from the 1 st-5th weekpost drug administration in vaccinated chickens when compared with thevaccinated control group.The chemotaxis index of macrophages was similarly affected inboth vaccinated and non-vaccinated groups as previously mentionedwith nonspecific and specific rnitogens .