A review of bioaerosol exposures and their potential health risks was presented. The review was a summary of conclusions reached by a workshop sponsored by the Composting Council, the Environmental Protection Agency, the Department of Agriculture, and NIOSH that was convened in January 1993 to consider possible adverse health effects caused by occupational exposure to bioaerosols generated by composting activities. The review described the characteristics and properties of compost bioaerosols, discussed the effects of nonoccupational and occupational exposures to compost bioaerosols, Aspergillus-fumigatus and other fungal aerosol exposures occurring in household environments, and the results of composting site, solid waste composting, yard waste, and individual case studies. Possible designs for composting facilities that could mitigate bioaerosol exposures were discussed. Problems and limitations encountered in measuring bioaerosols and techniques for performing risk assessments for compost bioaerosol associated illnesses were considered. The current state of knowledge of dose response relationships on the effects produced by the components of compost associated bioaerosols such as endotoxins and Aspergillus-fumigatus was reviewed using data obtained in studies that investigated the acute and chronic effects of compost bioaerosol exposures. Recommendations for future research on the health effects of compost generated aerosols were presented. Information on the waste composting industry in the United States and case definitions for diseases caused by A- fumigatus such as acute allergic alveolitis, asthma, and invasive aspergillosis were presented in appendices.