The risk of humans acquiring pneumonia as a result of their occupation appears to have declined during the twentieth century in developed countries, such as the United States. Thus, some conditions that are traditionally associated with the workplace, such as woolsorters' disease, represent illnesses that are of historical interest only. Nevertheless, the problem of occupation-associated pneumonia remains substantial. First, large outbreaks of zoonotic infections continue to occur, especially psittacosis among poultry farmers and abattoir workers. Second, clusters of illnesses caused by recently recognized pathogens are now being reported, including legionnaires' disease in industrial workers and Chlamydia pneumoniae infections in military personnel. Finally, epidemics of old conditions are appearing in new settings, such as tuberculosis among nursing home workers. Thus, the transmission, control, and treatment of pneumonias acquired in the workplace represent intriguing and challenging areas of concern to the epidemiologist and clinician.