White Leghorn chicken (Gallus domesticus) eggswere injected prior to incubation with one of four concentrations (0.001,0.01, 0.1, and 1.0 egg-equivalent) of an extract derived from 1,000double-crested cormorant (Phalacrocorax auritus) eggs collected atSpider Island adjacent to Green Bay in Lake Michigan. One egg-equivalentcorresponded to the concentration of contaminants present in an averagecormorant egg. This was approximately 322 pg toxic equivalents (TEQs)/g, wwegg with polychlorinatedbiphenyl congener 126(3,3',4,4',5-pentachlorobiphenyl) accounting for over 70% of the TEQs.Injection of 1.0 egg-equivalent resulted in 77% mortality at hatch.The incidence of developmental abnormalities (structural defects or edema)was not affected by injection of the extract. Body weight gain of chicks wasreduced in the 1.0 egg-equivalent dose group in the first, second, and thirdweek's post-hatch. Relative brain weights were greater and relativebursa weights were less in the 1.0 egg-equivalent dose group than in thevehicle control at three weeks of age. There were no significant differencesin the relative weights of the heart, liver, spleen, testes, or comb amongtreated and control birds.