Results are presented of a study on the uptake and metabolism of three pure **1**4C PCB's, DDT, and DDE by the green sunfish. It has been established that 2, 5, 2 prime -trichlorobiphenyl is quite susceptible to metabolism by the green sunfish, and 2, 5, 2 prime , 5 prime -tetrachlorobiphenyl and 2, 4, 5, 2 prime , 5 prime - pentachlorobiphenyl are much less susceptible. These latter two chlorinated biphenyls, especially the pentachloro isomer, resemble the relatively metabolic inert chlorinated hydrocarbons DDt and DDE.