In this study, polychlorinated biphenyl (PCB) concentrations were measured in great blue heron (GBHE) (Ardea herodias) chicks and eggs at Crab Orchard National Wildlife Refuge (CONWR) in southern Illinois. In addition, biomagnification factors (BMFs) from gizzard shad (Dorosoma cepedianum) and their effects on reproductive effort were examined. Total PCBs (SigmaPCBs) in chicks and shad were greater at the east end of Crab Orchard Lake (i.e., near the site of contamination) than the west end, but chick concentrations (4.1 to 10.1 mg/kg lipid weight) were lower than those typically associated with adverse effects. Chick BMFs based on shad from diet samples were greater than those based on shad collected from the lake. Furthermore, the two shad sources had dissimilar dioxin-like congener patterns and SigmaPCBs, suggesting that there was variation in PCB load and composition and that the more contaminated shad were a small proportion of the actual heron chick diet. The number of eggs laid per nest was similar between colonies, suggesting no observable population level effects. Further study may be necessary to evaluate long-term effects on GBHEs at CONWR.