310 one day old Ross chicks were used to study the effect of Chlortetracycline as a growth promoter (200 gm/ton ration) and/or Levamisole (20 mg/kg b.w.} on the immune response of chickens either non-vaccinated or vaccinated against New- castle disease virus. Chlortetracycline was found to increase the body weight and food consump­tion, and to improve the feed conversion ratio and feed effeciency, but it decreased the cellular immune response represented by decreased lYmphocyte stimulation index against phytoheamagglutinin, phagocytosis percentage and phago­cytic index. Also, it decreased the humoral immune response represented by decreased anti­body titre (ELISA titre) and decreased protection rate of the Newcastle vaccine against challenge with virulent ND • virus. While, levamisole in­ creased all the parameters of the cellular and humoral immune response in the chickens treated with both chlortetracycline and levamisole, thus assuring the levamisole immunorestorative properties