A physician should determine the ability to use a respirator, taking into account the employee's health, the respirator, and the work conditions. This report reviews the effects of respirator wear and provides referenced, reasonable guidelines for determining a worker's fitness to wear a respirator. The effects discussed include pulmonary, cardiac, body temperature, diminished senses, psychological reactions, and local irritation. Examining physicians should realize that heavy exercise with a respirator usually causes stress primarily on the cardiovascular system and that heavy (eg, self-contained, atmosphere-supplying) respirators can substantially increase this stress. Accordingly, exercise stress tests, with ECG monitoring, should be considered in these circumstances when cardiovascular risk factors are present. Available literature is noted that should help physicians screen prospective workers for the ability to use respirators.