 because of rampant concern that estrogenic chemicals in the environment may be adversely affecting the health of humans and wildlife , reliable methods for detecting and characterizing estrogenic chemicals are needed . 
 it is important that general agreement be reached on which tests to use and that these tests then be applied to the testing of both man - made and naturally occurring chemicals . as a step toward developing a comprehensive approach to screening 
 chemicals for estrogenic activity , three assays for detecting estrogenicity were conducted on 10 chemicals with known or suspected estrogenic activity . 
 the assays were 1 ) competitive binding with the mouse uterine estrogen receptor , 2 ) transcriptional activation in hela cells transfected with plasmids containing an estrogen receptor and a response element , and 3 ) the uterotropic assay in mice . 
 the chemicals studied were 17 beta - estradiol , diethylstilbestrol , tamoxifen , 4-hydroxytamoxifen , methoxychlor , the methoxychlor metabolite 2,2-bis(p - hydroxyphenyl)-1,1,1-trichloroethane ( hpte ) , endosulfan , nonylphenol , o , p'-ddt , and kepone . 
 these studies were conducted to assess the utility of this three - assay combination in the routine screening of chemicals , or combinations of chemicals , for estrogenic activity . 
 results were consistent among the three assays with respect to what is known about the estrogenic activities of the chemicals tested and their requirements for metabolic activation . by providing information on three levels of hormonal activity 
 ( receptor binding , transcriptional activation , and an in vivo effect in an estrogen - responsive tissue ) , an informative profile of estrogenic activity is obtained with a reasonable investment of resources.imagesp1296-afigure 1.figure 2.figure 3.figure 4.figure 5 . 
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