The presence of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) in feral lake trout eggs (Salvelinus namaycush) may increase the risk of lake trout early life stage mortality in the Great Lakes. To assess the combined toxicity of PCDDs, PCDFs, and PCBs to lake trout early development, toxic potencies, relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), were determined for individual PCDD, PCDF, and PCB congeners, based on rainbow trout (Oncorhynchus mykiss) early life stage mortality. Newly fertilized rainbow trout eggs were injected with graded doses of 2,3,7,8-TCDD, or a PCDD, PCDF, or PCB congener. LD₅₀ values were determined based on the egg dose that caused mortality from hatching onset to swim-up. Toxic equivalency factors (TEFs) were calculated as 2,3,7,8-TCDD LD₅₀/congener LD₅₀. TEFs were for PCDDs: 2,3,7,8-TCDD = 1.0; 1,2,3,7,8-PeCDD = 0.730;and 1,2,3,4,7,8-HxCDD = 0.319; for PCDFs: 2,3,4,7,8-PeCDF = 0.359; 1,2,3,4,7,8-HxCDF = 0.280; 1,2,3,7,8-PeCDF = 0.034; and 2,3,7,8-TCDF = 0.028; and for PCBs: 3,3',4,4',5-PeCB = 0.005; 3,3',4,4'-TCB = 0.00016; 2,3,3',4,4'-PeCB and 2,3',4,4',5-PeCB < 0.00007. For PCDDs, fish-specific TEFs were 10- to 100-fold higher than TEFs determined in H4IIE rat hepatoma cells, but were similar to TEFs proposed for risk assessment. For PCDFs, fish specific TEFs were similar to TEFs determined in H4IIE cells and TEFs proposed for risk assessment. However, the most significant finding was that for the coplanar PCBs and mono-ortho-chlorinated analogues of the coplanar PCBs fish-specific TEFs were 1/14 to 1/80 less than both those determined in H4IIE cells and proposed for risk assessment. Using these fish-specific TEFs, the risk associated with exposure of early life stages of Sake trout to complex mixtures of PCDDs, PCDFs, and PCBs in the Great Lakes can be estimated.