The purpose of this study was to evaluate the physiological performance of a liquid cooling garment in controlling heat stress in individuals wearing Hazmat protective ensembles. Five heat-acclimated male subjects completed three trials each: standard work clothing (WC), Hazmat suit (H), and a Hazmat suit with torso cooling (HC). All testing took place in an environmental chamber (35°C and 50 % relative humidity) with subjects walking on a treadmill at a metabolic rate of 300 W. Trials were performed until subjects completed the maximum 90 min, achieved the predetermined endpoints in core temperature (38.5°C) or heart rate (95 % of age predicted maximum), or symptoms of fatigue, disorientation, and discomfort forced the participant to discontinue or the researchers to end the test. A significant difference (P<0.05) between HC and H was found in final heart rate and core temperature (T^re), rate of change in heart rate and T^re, and exposure time. As well, HC was similar to WC in all measured physiological variables. It was concluded that a liquid cooling vest was beneficial in alleviating the heat stress caused by Hazmat protective ensembles.