Eggs from four species of aquatic birds inhabiting waterways of the Lake St. Clair region were collected in 1973 and analyzed for mercury. Species analyzed were mallard ducks (Anas platyrhynchos), common terns (Sterna hirundo), black-crowned night herons (Nycticorax nycticorax), and great egrets (Casmerodius albus). Mallard eggs contained relatively low residue levels, less than 0.05-0.26 ppm, and common tern eggs contained the highest residues, ranging up to 1.31 ppm. Mercury levels in the eggs were appreciably lower than those in the same species in 1970. The declines are attributed to the 1970 restrictions placed on industrial discharges of mercury into the St. Clair and Detroit Rivers.