Toxic equivalency factor (TEF) approaches have been used to evaluate the reproductive hazards of polychlorinated biphenyls (PCBs) to wildlife. These approaches are based primarily on the relative potency of individual PCB congeners for 2,3,7,8-tetrachlorodibenzo-p-dioxin-like induction of ethoxyresorufin-O-deethylase (EROD) enzyme activity. One of the primary concerns in this practice is the fact that induction of EROD activity has not been mechanistically linked to the occurrence of any adverse effect. Other PCB-induced enzyme activities are more plausibly linked to mechanisms of potential reproductive toxicity. For example: some PCB-induced enzymes are responsible for altered metabolism of androgens and estrogens. Induction of these enzymes by dioxin typically requires much greater doses than does EROD. Consequently, an EROD-based TEF approach is likely to over-estimate potential reproductive health risks to wildlife, perhaps by as much as several orders of magnitude.