Methionine (Met) and arginine (Arg) play crucial roles in maintaining poultry health and performance beyond protein synthesis. This dissertation presents findings from four studies investigating the effects of Met and Arg supplementation on broiler intestinal and bone health during coccidiosis challenge or concurrent coccidiosis and heat stress. In the first study, effects of altering the methionine to cysteine ratio (MCR) on broiler performance, intestinal health, and bone quality during coccidiosis challenge was examined, the results suggested that partially replacing Met with Cys at a MCR of 75:25, did not deteriorate the performance or intestinal health of the broilers. It was also found that increasing the MCR could lead to worsened bone quality of the birds. The second study investigated effects of linearly increased dietary Met concentrations in normal or reduced protein diets on broilers during coccidiosis challenge. Findings indicated that dietary Met concentrations higher than 6.0 g/kg did not necessarily improve broiler performance or intestinal health under coccidiosis challenge. The results further revealed that increased Met concentrations decreased femoral cortical bone quality, it improved trabecular bone quality in reduced protein diets. The third study investigated Arg supplementation in reduced protein diets during coccidiosis challenge. Results showed that Arg supplementation reversed the negative effects of reduced protein diets on growth performance and intestinal health, with beneficial impacts on immune responses. The last experiment investigated the effects of Met or Arg supplementation in reduced protein diets on broiler under concurrent coccidiosis and heat stress (HS). The results indicated that HS may mitigate coccidia infection severity but still reduced growth performance. Reduced protein diets improve intestinal health during acute coccidiosis and HS, with Arg supplementation further enhancing growth performance. In conclusion, this dissertation suggested that while Met is essential for its antioxidative effects and maintaining normal growth performance, higher Met could lead to worse bone quality, and a MCR of 75:25 and dietary Met concentration of 6.0 g/kg was recommended for broilers under coccidiosis challenge. However, current recommended Arg concentrations may be insufficient for broilers under challenge conditions, and supplementing extra Arg is beneficial for their health and performance under such conditions.