Abstract: The research work was conducted to investigate the serum antibody response againstListeria ivanoviiin experimentally infected rabbits by inoculation method. It was found out that the blood monocyte count was increased, from 2-3% (prior injection) up to 15% to 72 hours post injection and the count declined after 120 hours. There was a significant rise in mononuclear cells after the repetition of doses except that the level was maintained during these intervals. The highest antibody level was observed at 14-15 days post-inoculation, which persisted for more than three months. These findings suggest that an association exists between the increased number of monocytes in the blood and humoral immune response in correlation with the resistance against listeric infection.