Compared levels of organochlorines, mercury and lead in Pandion haliaetus eggs and potential prey from Delaware Bay to a successful population along the Atlantic Coast (<80 km from the Bay colony) and a geographically intermediate population along Maurice River (<40 km from the Bay colony), a tributary of Delaware Bay. Eggs from Delaware Bay contained significantly higher levels of DDE, DDD, PCB's, dieldrin, and heptachlor epoxide than did Atlantic Coast eggs and also had thinner eggshells; eggs from Maurice River had intermediate contaminant levels and eggshell thickness. Contaminant levels in potential prey from each region reflected levels found in eggs, suggesting that ospreys accumulated contaminants on their breeding grounds. Eggshell thickness was most closely correlated with levels of DDD and DDE in eggs. With the exception of dieldrin, addled and randomly collected eggs contained similar contaminant levels, although addled eggs contained mirex more frequently.