Bronchospasm is a common cause of morbidity in the workplace. More than 100 agents are now recognized as occupational causes of asthma and numerous agents can cause exacerbations of preexisting asthma. Because of the large number of potential causative agents and the complexity of modern industrial processes, knowledge of the characteristic clinical features of occupational asthma is the key to recognizing this disease. Early diagnosis of occupational asthma is important in preventing long-term morbidity. Present evidence that prolonged exposure to some work-encountered agents can cause asthma that persists for years after the end of exposure suggests that avoidance is the only acceptable countermeasure against this disease.