identification of major dioxinlike compounds and androgen receptor antagonist in acidtreated tissue extracts of high trophiclevel animals we evaluated the applicability of combining in vitro bioassays with instrument analyses to identify potential endocrine disrupting pollutants in sulfuric acidtreated extracts of liver andor blubber of high trophiclevel animals dioxinlike and androgen receptor ar antagonistic activities were observed in baikal seals common cormorants raccoon dogs and finless porpoises by using a panel of rat and human cellbased chemicalactivated luciferase gene expression calux reporter gene bioassays on the other hand no activity was detected in estrogen receptor er glucocorticoid receptor gr progesterone receptor pr and peroxisome proliferatoractivated receptor 2 ppar2calux assays with the sample amount applied all individual samples n 66 showed dioxinlike activity with values ranging from 21 to 5500 pg calux2378tetrachlorodibenzopdioxin equivalent teqglipid because dioxins are expected to be strong contributors to caluxteqs the median theoretical contribution of dioxins calculated from the result of chemical analysis to the experimental caluxteqs was estimated to explain up to 130 for all the tested samples n 54 baikal seal extracts n 31 but not other extracts induced ar antagonistic activities that were 8150 g caluxflutamide equivalent flueqglipid ppdde was identified as an important causative compound for the activity and its median theoretical contribution to the experimental caluxflueqs was 59 for the tested baikal seal tissues n 25 our results demonstrate that combining in vitro calux assays with instrument analysis is useful for identifying persistent organic pollutantlike compounds in the tissue of wild animals on the basis of in vitro endocrine disruption toxicity