A total of 400 pieces of day-old male broiler chicks were distributed into 9 treatments and one control diet with 4 replicates using a CRD design (3x3 factorial). Chicks for 42 days received graded levels of Cu (35, 70, 105 mg kg-1 diet) and Zn (40, 80, 120 mg kg-1 diet) in their diets (free of Cu and Zn mineral premix) to determine the antibody titer of SRBC and the weights of lymphoid organs (BW%) including: Thymus (TW), Bursa (BW), Spleen (SW) and Liver (LW). On days 28 and 35, two birds from each pen received SRBC (1 mL, 10%) injections and were bled 7 days after each inoculation to evaluate the primary and secondary responses for Total Immunoglobulin (TIg), Immunoglobulin M (IgM) and Immunoglobulin Y (IgY). On day 42, two birds from each pen were slaughtered to weigh the lymphoid organs. Since analysis of data showed no significant interaction between graded Cu and zinc, only the main effect of means were considered. The graded Cu increased titers of TIg and IgY linearly but reduced IgM titer quadratically in primary response. In secondary response, the titers of TIg and IgM decreased, but IgY increased quadratically. The graded Zn increased TIg and decreased IgM titers quadratically but the titer of IgY increased linearly in primary response. In secondary response, the graded Zn increased IgM titer but decreased TIg and IgY titers quadratically. The graded Cu enhanced TW and SW linearly but BW and LW (p<0.05) quadratically. The graded Zn increased TW and decreased BW linearly but decreased SW and LW quadratically. Overall results indicated that adding Cu at 70-105 ppm and Zn at 80-120 ppm improved SRBC titers and weights of lymphoid organs. In conclusion, adding Cu and Zn at recommended levels can be useful as immunomodulators in broiler chicks.

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