Morphological and biochemical indexes of contaminant exposure were examined in hatching common terns (Sterna hirundo) and black-crowned night herons (Nycticorax nycticorax) from industrialized and nonindustrialized locations in the Great Lakes. In 1984, naturally incubated, pipping common tern and black-crowned night heron embryos collected from industrialized locations exhibited smaller femur-length-to-body-weight ratios, elevated hepatic microsomal aryl hydrocarbon hydroxylase (AHH) activities, and lower hepatic DNA concentrations (P < 0.05). In addition, a high incidence of subcutaneous edema was noted in pipping herons (P < 0.01). In 1985, reduced hatching success was observed for laboratory-incubated common tern eggs collected from the industrialized sites, compared to nonindustrialized sites (P < 0.01). Day-old hatchlings exhibited reduced femur-length-to-body-weight ratio, developmental anomalies, and elevated hepatic AHH activity (P < 0.05). For hatching common terns studied in 1984 and 1985, femur-length-to-body-weight ratio was inversely related to AHH activity (r = −0.67, P < 0.05) and inversely related to log-transformed PCB concentrations (r = −0.70, P ≤ 0.05) of unincubated eggs from the same colony. The activity of AHH in hatching terns was also directly related (r = 0.71, P ≤ 0.05) to log-transformed PCB concentrations in unincubated eggs. Other examined contaminants, including DDE, other organochlorine pesticides, and mercury, were not directly related to these effects.