The objective of this study was to investigate the effects of vitamin C and alpha-lipoic acid dietary supplementations for 42 days on metabolic response of broilers to heat stress during entire feeding period. Whereas negative control birds were kept to 24 degrees C as ambient temperature, heat stressed broilers fed with basal diets (stress positive controls) and supplemented with vitamin C (250 mg/kg/day) or with alpha-lipoic acid (250 mg/kg/day) were exposed to 34 degrees C for 8 hours every day. Serum biochemical markers, serum lipid profiles, blood gas analysis and acid-base regulation were assessed at the end of the experimental period. Despite the long term heat exposure, serum concentrations of glucose, total proteins, albumin, globulins, lipids (triglycerides, cholesterol and lipoproteins), electrolytes (Na+, K+ and Cl-) and iron as well as serum liver enzyme (AST, ALT, GGT and ALP) activities were not significantly altered compared to the negative controls. By contrast, pancreatic amylase activity was dramatically increased, the uric acid and Mg concentrations were significantly declined and Ca and P concentrations also tended to decrease in birds exposed to heat stress. In parallel, the respiratory rate was markedly accelerated leading to amplification in blood gas exchanges (significant increase in pO(2), weak decrease in pCO(2) and in HCO3- concentrations, weak increase in blood pH) and to significant reduction in haemoglobinemia. In addition, alpha-lipoic acid supplementation has significantly changed serum lipid profiles by increasing the triacylglycerol proportions and decreasing the free fatty acid and polar lipid percentages. Dietary supplementations with vitamin C and mainly with alpha-lipoic acid have not significantly modified blood gas exchanges and acid-base equilibrium but have partly corrected the metabolic response.