The effects of the use of respiratory protective masks were investigated in 20 volunteers, using a system designed to permit the measurement of ventilatory parameters by respiratory inductive plethysmography (RIP). The RIP equipment measured respiratory frequency, tidal volume, minute ventilation, and heart rate. Three men were steel mill employees who worked at a blast furnace and wore long shirts, pants, and work boots. When working with the molten ore, they also wore a dual cartridge, half face respirator, and an aluminum coated hooded garment. Employees from two equipment repair facilities included eight sandblasters, six spray painters, and two other workers. Sandblasting employees wore coveralls with an airline respirator hood with cooled inspired air in a large enclosed bay. The four spray painters used airline respirators and two wore dual cartridge, full face respirators. The other two workers used half face dual cartridge respirators in sanding or cleaning activities. In general, the cardiopulmonary parameters increased during respirator wear. The findings of the study suggest that during respirator required work, changes in work level, protective clothing, and ambient heat stress were important stress factors in addition to the effects of the respirator itself. The authors stress the need to consider all aspects of the respirator work situation in assessing the physiological and subjective stress to the employees. Respirator wear increases the respiratory frequency and minute ventilation. Further improvements in the portable monitoring of cardiopulmonary parameters are needed.