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 wereFirst experiment:45 mice were inoculated by attenuated virus. We madefollow up for virus isolation from liver and serum every 48 hours.We made also follow up for antibodies. It was found that the. attenuated virus presented in serum for 8 days and disappearedafter that. The virus appears in the liver at 6day and persisted tillthe end of experiment. Antibodies appeared at 8th day andincreased until the end of experiment.Second experiment:15 pregnant mice were used ”at last 5 days of gestation”.Which were divided into 5 groups, 1 st four groups ”I, 11, III and IV”were inoculated by the attenuated virus in different doses, the actof parturition under the effect of attenuated virus were observed.All mothers were delivered normally without problems. After 21days the newly born were challenged, the off springs overcomethe virus by different degrees and this mean that the immunity maybe transmitted through out placenta or milk and make protection ofthe offspring.