A wetland in central Arkansas was contaminated with polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans and because the area was a major waterfowl habitat, we studied the effects of the contamination on nesting wood ducks (Aix sponsa) during 1988-90. Residues in wood duck eggs, based on toxicity equivalency factors (TEFs) for combined compounds, ranged from 0.2 to 611 parts per trillion (ppt) wet mass (70% were the toxic isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (tetraCDD)) and were 50 times higher in eggs from near the point source than from an uncontaminated reference site 111 km away. Nest success, hatching success, and duckling production were suppressed (P lt 0.05) at nesting sites 9 and 17 km downstream, as was hatching success 58 km downstream. Egg TEFs were inversely correlated (P lt 0.001) with productivity in corresponding nests. In addition, teratogenic effects occurred in ducklings at the more contaminated nesting site nearest the point source. The threshold range of toxicity (based on TEFs) where reduced productivity was evident in wood ducks was gt 20-50 ppt. Wood ducks were sensitive to dioxin and furan contamination, and we recommend it as an indicator species for monitoring biological impacts from these contaminants.