Most firefighters wear heavily insulated rubber boots or lighter leather boots. A five to 12% increase in oxygen consumption per kg of weight added to the foot has been observed; however, the increase may depend on gender, boot material, and whether or not subjects are wearing additional protective clothing or equipment. PURPOSE: To determine the effects of two leather (L1, L2) and two rubber (R1, R2) boots on firefighters' metabolic and respiratory variables during simulated firefighting tasks. METHODS: Eighteen women and 21 men, while wearing full turnout gear and one of four randomly assigned pairs of firefighter boots, walked for six minutes at three mph on a treadmill while carrying a 9.5-kg hose and then climbed a stair ergometer for six minutes at 45 steps/min. Minute ventilation (VE), oxygen consumption (VO2 and VO2kg), CO2 production (VCO2), and heart rate (HR) were measured, and an average of breath-by-breath data from minute six was used for analysis of covariance with repeated measures. RESULTS: During treadmill exercise, boot weight had a significant effect (p . 0.05) on VO2 and VO2kg for men only, whereas boot weight had a significant effect (p . 0.05) on VE and VCO2 for both men and women. There were no significant effects of boot weight during stair climbing. There were no significant effects of boot material on any variables during either mode of exercise. CONCLUSION: During treadmill exercise, each additional kg of boot weight was associated with a significant 6.5% increase in VE for both men and women and with a significant 8% increase in VO2 and VO2kg for men only.