Abstract INTRODUCTION A REVIEW of the literature indicates that comparisons between laying and non-laying hens under heat stress conditions are very limited. Huston et al. (1957) indicated that at high environmental temperature 32.2°C. (90°F.), nonlayers had 0.4°C. (0.7°F.) higher body temperature than layers, which was highly significant. The body temperature of layers and non-layers held in the variable temperature environment was identical. Hillerman and Wilson (1955) reported that layers had a higher body temperature than non-layers. However, most heat stress research has been reported with hens in which the laying condition was not mentioned. Wilson (1948), using Single Comb White Leghorns, indicated that if the air temperature was 40.6°C. (105°F.), it was impossible to keep all birds alive for more than six hours. Lee et al. (1945) and Wilson (1948) observed that a rectal temperature of 45°C. (113°F.) is the uppermost limit of safety for hens. Randall and Hiestard (1939), using…