Tetra-to decachlorodiphenyl ether (CDPE) concentrations were measured in lake trout and walleye, fish that represent the higher trophic levels in the North American Great Lakes GC MS analyses indicated the mean total CDPE concentrations were 4, 16, 57, and 126 kg/kg in whole fish from Lakes Superior, Huron, Erie, and Ontario, respectively The number of known and unidentified congeners detected above the 0 4 pg/kg detection limit ranged from six to 24 congeners among the lakes, and this number increased with the total concentration of CDPEs The C1, homologue represented 46 to 61% of total CDPEs in Lakes Huron, Erie, and Ontario, and the CIS, Cl,, and C1, homologues represented 78 to 93% of total CDPE concentrations About 83 to 91% of total CDPEs detected in these samples were identified from analytical standards Rank correlation analyses indicated no significant differences among the relative concentration patterns of congeners in Lakes Ontario, Erie, and Huron fish A similar congener pattern was not shown in Lake Superior fish because of relatively higher contributions from unidentified C1, and CI,-DPEs