EFFECTS of fed supplements, sodium bicarbonate (NaHCO₃), Ascorbic acid (Vitamin C) and Vitamin E were evaluated on the performance, immune system and biochemical parameters of chronically heat-stressed broiler chicks. Two hundred day old broiler chicks were allotted to one of the five groups (n = 40),(A) normal control [no supplements], (B) heat stressed [no supplements], (C) NaHC0₃,2g/kg diet, (D) Vitamin C, 200mg/kg diet and (E) Vitamin E, 300 mg/kg diet. All chicks except group (A) were maintained at 35-40 ºC from day one to 6 weeks (wks) of age (daily 6 hrs heat stress episodes). Samples were taken at 2,4 and 6 weeks of age. The result showed Significantly higher bodyweight gains were recorded in all supplemented groups as compared to control group with better response in birds fed sodium bicarbonate (NaHCO₃ ) .Bursal index, percentage weights of thymus and spleen in relation to body weight, an indicator of humoral immunity were higher but the heterophil / lymphocyte ratio, an indicator of stress was lower for the all supplemented groups as compared to control group .The dietary supplement significantly increased antibody titer of ND and AI on day12 post  vaccination (P<0.05). However, dietary vitamin E had higher effect on antibodies titer compared to other groups. In heat stressed group serum uric acid, urea, glucose, AST, ALT increased significantly (P ≤0.05) while blood Na and K and total proteins, albumin, globulin, decreased significantly (P<0.05) from respective control mean values.There were no significant (P>0.05) effects of supplemental sodium bicarbonate (NaHCO₃), Ascorbic acid (Vitamin C) and Vitamin E on plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Overall, the results indicated significant improvement in the performance and immune response of chronically heat-stressed broiler chicks given the feed supplements, ascorbic acid supplementation enhanced the hematological profile of birds but generally, NaHCO₃ being slightly superior to Vitamin C and Vitamin E.