1. The objective was to evaluate the effects of brooding temperature on intestinal development, oxidative organ damage, and performance of chicks acclimated to high temperature during incubation. The effects of acclimation and brooding temperatures on slaughter weights of broilers under heat stress were also investigated. 2. Eggs were incubated at either 378 degrees C (INCCont) or heat-acclimated at 395 degrees C for 6 h daily from d 10 to d 18 of incubation (INCH). Brooding temperatures at floor level were set at 32, 335 and 35 degrees C (Bt32, Bt335, Bt35, respectively) for the first 5 d. The temperature was reduced gradually to 30 degrees C from d 6 to d 10. From 21 to 42 d, broilers from INCCont Bt32 and INCH Bt32 and Bt35 were divided into two groups; half from each group was exposed to daily cyclic higher ambient temperatures, while the other half was reared at control temperature. 3. INCH chicks had lower jejunum, but greater liver and residual yolk sac weights than INCCont chicks on the day of hatching. Although INCH chicks from Bt335 and Bt35 had lighter body weights than Bt32 on d 5, no significant differences were observed in the body weight of broilers among treatments at 10 and 21 d. 4. Similar jejunum protein, alkaline phosphatase, maltase, glutathione, and malondialdehyde contents of chicks from INCCont and INCH suggested that heat acclimation during incubation has no effect on jejunum enzyme activity or oxidative status of chicks. 5. Taking into account INCH Bt35 chicks having lower T3 levels on d 5, lower heterophil/lymphocyte (H/L) ratios and similar weights at 42 d under heat stress compared with control broilers, the results suggested that although higher brooding temperatures had no effect on body weights of INCH chicks during the brooding period, those broilers may able to cope better with heat stress.