The primary objective of this research was to determine the health effects, if any, associated with occupational exposure to biological agents present in municipal wastewater. An additional objective was to determine the sensitivity of the methodology for detecting potential health impacts of other wastewater exposures such as recreational contact with surface water receiving wastewater effluents. The procedure was a prospective seroepidemiologic study applied to municipal wastewater workers and controls in three metropolitan areas: Cincinnati, Chicago, and Memphis. A total of over 500 volunteers participated in the study including both subjects and controls. The protocol involved: quarterly collection of blood, throat and rectal swabs; yearly medical examinations; collection of illness information; work observations; and environmental monitoring. Final specimens in all cities were collected in the fall of 1978. The serological survey included testing for antibodies to a large group of viruses and bacteria and determination of immunoglobulin levels. Work observations were used to evaluate the level of the workers' contact with wastewater and, in conjunction with the biological air monitoring, to assess the extent of contact with aerosols. The environmental monitoring included viral and bacterial analyses of wastewater and the use of six stage Andersen samplers to determine respirable concentrations of bacteria in the work area of the plant.