Preferential biomagnification of 14 dioxin-like polychlorinated biphenyls (PCBs) was determined in lower-trophic-level organisms of the Lake Michigan, USA, food web. Bioaccumulation of these coplanar, aryl hydrocarbon hydroxylase (AHH)- inducing PCB congeners and total PCBs in phytoplankton, zooplankton, Mysis relicta, and Diporeia sp. were studied for two locations in Lake Michigan over time. The results indicate that both total PCB and AHH-inducing PCBs biomagnify with increasing food web trophic level, with biomagnification of the AHH-inducing PCBs occurring to a greater degree. The biomagnification factors (BMFs) of the AHH-inducing PCBs suggest that they are highly conserved relative to other PCB congeners. The concentrations expressed as dioxin toxic equivalencies (TEQ concentrations) indicate that the biomagnification of AHH PCBs causes greater concentrations, and thus greater toxicity risk, with increasing trophic level.