Constant-wear anti-exposure suit ensembles, employing a polytetrafluoroethylene (PTFE) coverall, were evaluated for their impact on aircrew performance under heat stress. Conditions were designed to simulate stresses experienced by aircrews during aircraft operations over cold water; therefore, chamber temperatures were maintained at dry bulb temperature = 34.0 +/- 1.5 degrees C and wet bulb temperature = 23.9 +/- 4.5 degrees C. Six subjects were studied twice in each of five configurations, i.e., a standard flight ensemble (control), and four combinations of the PTFE coverall with different liners, for maximum 180-min exposures. Subjects alternated periods of physical work, performance of a psychomotor task, and rest, for a total time of 20 min in each activity cycle, which were repeated throughout the duration of a trial, at an estimated mean metabolic rate of 2.4 kcal.min-1. Mean test duration for the control was 177 +/- 9 min, while for the other configurations, mean test durations were 105 +/- 32 min, with no significant differences observed between the PTFE-based configurations. Total sweat rate (SRT), heat storage rate (S), final heart rate (HR), and mean weighted skin temperature (Tsk) indicated similar trends among configurations, with significant differences principally observed as a consequence of the use of the PTFE coverall. Use of the PTFE coverall appears to limit heat tolerance to less than 3 h if a moderate workload is imposed under heat stress.