Respiratory protection is a complex field involving industrial hygiene, physics, physiology, toxicology, medicine, anthropology, engineering, law, and worksite administration. Although the use of respirators is widespread, they are the least effective and often the most costly method of protecting workers. Preferred methods of protection are engineering controls that eliminate exposure and substitution of the agent for one of lesser toxicity. However, in work situations where alternative methods are not available, a well-designed and well-monitored respiratory protection program can still provide a safe environment for the soldier and civilian worker. With the enactment and enforcement of the Occupational Health and Safety Act, worker protection has gained a much higher priority among employers and health officials. The field is dynamic and some of the medical screening procedures outlined in TB MED 502 (Respiratory Protection) are outdated. Industrial processes and state-of-the-art protective equipment change rapidly. Because certified occupational health physicians and nurses are not always available, health care workers need a fundamental understanding of respiratory protection.