Eggs and sibling 1-, 3-, and 5-d-old chicks from seven black-crowned night-heron (Nycticorax nycticorax) broods were collected from Green Bay, Wisconsin, and analyzed for organochlorines. The concentration (A?g/g) of nine organochlo-rines either decreased (n = 7) or remained the same (n = 2) as the chicks grew older. In contrast, the total mass (A?g) of these nine organochlorines increased (n = 7) or remained the same (n = 2) as the chicks grew older. Accumulation rates of mass (A?g/d) between egg and 5-d-old chicks for each of the nine organochlorines were positive and varied from 0.2 A?g/d (p,pa??-DDT) to 42 A?g/d (PCBs). These results suggest that the loss of contaminant mass from eggs to chicks reported in some earlier studies was because the entire carcass was not analyzed (i.e., not including skin, gastrointestinal tract, etc.). These results also support the use of contaminant accumulation rates as an indicator of local contamination.