A cross sectional industrial hygiene and medical study was conducted at a mushroom farm in Florida where seven cases of mushroom worker's lung (MWL), a form of hypersensitivity pneumonitis, were reported between April 1982 and August 1985. Typically, the episodes started with mild symptoms which increased in severity and frequency, culminating in a severe attack. Severe attacks were characterized by shortness of breath, fever, chills, dry cough, fatigue, malaise, muscle aches, and breathing difficulties. While histopathologic findings were consistent with hypersensitivity pneumonitis, antibody tests yielded no clear and consistent differences between cases and comparisons. The industrial hygiene study consisted of a questionnaire, pulmonary function test, chest radiograph, and serologic testing. The 259 participating employees were divided into seven work groups: wharf workers, growing/watering workers, pickers, packers, maintenance workers, night workers, and office workers. While none of the workers were experiencing acute symptoms, 54 were considered possible cases. About 10% of both possible MWL cases and noncases had below normal spirometry tests. Over 40% of the tested workers reacted positively to extracts of stockpiled compost, but few had positive reactions to extracts of selected thermophilic actinomyces or fungi. No differences in precipitin reactions were evident. Pickers and packers (mostly women), nonsmokers, and workers with high tenure had higher proportions of positive reactions to Agaricus-bisporus spores, as measured by double diffusion and the enzyme linked immunosorbent assay. However, the radioallergosorbent test did not reveal any differences. The authors conclude that several different allergens may be responsible for causing MWL. The authors recommend that mushroom farm workers be counseled about the risks and symptoms involved, and that airborne antigens be kept as low as possible.