At the beginning of this study, broiler chicks experienced ideal conditions (30.6C, 35% RH), while reared in environmental chambers. Half the chicks were then housed at 24C and 35% RH, while the other half were exposed to cyclical temperature/RH management. The cyclical regime was a heat treatment and was used to simulate August in Mississippi. Within each group, half the birds were implanted with an osmotic pump that released adrenocorticotropin (ACTH). The other birds were implanted with placebo pumps. The ACTH and heat treatments caused decreased body weight, carcass weight, carcass protein and muscle calorie content. The ACTH treatment reduced carcass moisture. After a one-week recovery period, these changes did not reverse. The results indicated that both heat and hormonal induced stress caused severe losses similar to those associated with PSE found in commercial conditions.