While the primary purpose of thennal protective uniforms is to minimise heat loading from hostile working environments, such uniforms also add to the physiological load by increasing metabolic rate, and limiting evaporative heat dissipation (I). Before one can provide physiological specifications for the design of thennal protective garments, one requires a thorough understanding ofthe physiological effects of wearing such unifonns. However, research in this area is dominated by field studies, with few cardiovascular variables being investigated. These field studies, while important, often bypass clothing trials under controlled laboratory conditions. As a consequence, very little is known about the cardiac output, skin blood flow orplasma volume responses associated with wearing thermal protective clothing. Therefore, weundertook a laboratorybased project to explore the mechanisms underlying the cardiovascular strain accompanying the use of thermal protective ensembles, relative to the unclothed state, during fatiguing exercise. We hypothesised that subjects would experience greater cardiovascular strain when wearing such clothing, and that this would limit their ability to perform maximal exercise.