Impaired respiration reduces firefighters’ work capacity. This study evaluated the effect of menthol lozenge on respiratory and perceptual responses during exercise in a hot environment. Ten participants wearing firefighter protective gear performed two repeated exercise and rest trials in a counter-balanced order. Exercise consisted of two bouts of 20-min treadmill exercise at 60% of maximal oxygen uptake and one bout of 20-min stepping exercise at a wet bulb global temperature of 35°C. Participants either took 10-mg menthol or control lozenges prior to the beginning of each exercise bout. Respiratory gas exchange, heart rate, thermal sensation, and breathing comfort were continuously recorded. Menthol lozenges significantly increased pulmonary ventilation (menthol: 45.0±6.6 L•min-1 vs. control: 41.4±5.8 L•min-1 and menthol: 52.7±9.7 L•min-1 vs. control: 46.5±7.0 L•min-1, for the 1st and 2nd treadmill exercise, respectively) and oxygen consumption (menthol: 26.7±2.0 ml•kg-1•min-1 vs. control: 25.2±2.3 ml•kg-1•min-1 and menthol: 28.8±2.3 ml•kg-1•min-1 vs. control: 26.9±1.9 ml•kg-1•min-1, for the 1st and 2nd treadmill exercise, respe¬cti¬ve¬ly) (p<0.05). The effect of menthol on respiration disappeared during the stepping exercise (p>0.05). The ventilatory equivalents though were not different throughout the exercise (p>0.05). Ratings of thermal sensation and breathing comfort were not different (p>0.05). It was concluded that menthol could alter breathing pattern and increase respiratory responses during strenuous exercise in the heat. There was no favorable effect of menthol on respiratory or perceptual responses under exercise-heat stress.