ntroduction: Recent research has focused on developing air-ventilated garments to improve evaporative cooling in military settings. This study assessed a ventilated vest (Vest) in hot (45°C), dry (10% RH) ambient conditions over 6 h of rest and exercise. It was hypothesized that the Vest would lower the thermal strain and increase the amount of exercise done by subjects. Methods: Eight healthy heat-acclimated men, wearing combat clothing, body armor, and a 19-kg load in webbing walked on a treadmill at 5 km · h−1 at a 2% incline until rectal temperature (Trec) reached 38.5°C. They then rested until Trec reached 38°C, at which point they recommenced walking. On one occasion the subjects wore a Vest, blowing ambient air around the torso. On the second occasion subjects did not wear the vest (NoVest). Exercise/rest ratio, Trec, skin temperature (Tsk), sweat responses, rating of perceived exertion (RPE), and thermal comfort (TC) were measured. Results: Subjects wearing the Vest exercised for significantly longer (18%; 11 min/h) as a percentage of total exposure time, stopped exercise significantly less often [Mean (SD); NoVest: 3 (2) stops; Vest: 1 (2) stops], and maintained significantly lower skin temperature under the body armor [Tchest: NoVest 37.55 (0.51)°C; Vest: 35.33 (1.00)°C; Tback: NoVest: 36.85 (0.83)°C; Vest: 35.84 (0.88)°C]. The Vest provided 28 W of cooling during exercise and 73 W when at rest as estimated by thermometry. Conclusion: A ventilated vest can provide cooling, and thereby reduce thermal strain and increase exercise done in dry environmental temperatures up to 45°C, without causing skin irritation and discomfort.