Technical Abstract: The Chesapeake Bay osprey population has more than doubled in size since restrictions were placed on the production and use of DDT and other toxic organochlorine contaminants in the 1970's. Ospreys are not nesting in the most highly polluted portions of the Bay. In 2000 and 2001, contaminant exposure and reproduction were monitored in ospreys nesting in regions of concern, including Baltimore Harbor and the Patapsco River, Anacostia and middle Potomac Rivers, Elizabeth River, and a presumed reference site consisting of the South, West, and Rhode Rivers. A "sample egg" from each study nest was collected for contaminant analysis, and the fate of eggs remaining in each nest (n=14-16/site) was monitored at 7-10 day intervals from egg incubation through fledging of young. Ospreys fledged young in regions of concern (observed success: 0.88-1.53 fleglings/active nest), although productivity was marginal for sustaining local populations in Baltimore Harbor and the Patapsco River, and the Anacostia and middle Potomac Rivers. Concentrations of p,p'-DDE and many other organochlorine pesticides, total PCBs, some arylhydrocarbon receptor-active PCB congeners and brominated diphenyl ether congeners, and perfluorooctane sulfonate were often greater in sample eggs from regions of concern compared to the reference site. Nonetheless, logistic regression analyses did not provide evidence linking marginal productivity to p,p-DDE, total PCBs or arylhydrocarbon receptor-active PCB congener exposure in regions of concern. In view of moderate concentrations of total PCBs in eggs from the reference site, concerns related to new and emerging toxicants, and the absence of ecotoxicological data for terrestrial vertebrates in many Bay tributaries, a more thorough spatial evaluation of contaminant exposure in ospreys throughout the Chesapeake may be warranted.