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Many environmental contaminants alter the reproduction of animals by altering the development and function of the endocrine system. The ability of environmental contaminants to alter the endocrine system of alligators was studied both in a descriptive study in which juvenile alligators from a historically contaminated lake were compared to animals from a control lake and in an experimental study in which hatchling control alligators were exposed in ovo to several endocrine-disrupting standards and two modern-use herbicides. Endocrine status was assessed by examining plasma hormone concentrations, gonadal-adrenal mesonephros (GAM) aromatase activity, and gonadal histopathology. In the descriptive study, juvenile alligators from the contaminated lake had significantly lower plasma testosterone concentrations (29.2 pg/ml compared to 51.3 pg/ml), whereas plasma 17 beta-estradiol concentrations did not vary when compared to controls. GAM aromatase activity was significantly decreased n the alligators from the contaminated lake (7.6 pmol/g/hr compared to 11.4 pmol/g/hr). In the experimental study, the endocrine-disrupting standards had the expected effects. 17 beta-Estradiol and tamoxifen caused sex reversal from male to female, with a corresponding increase in aromatase activity. Vinclozolin had no apparent effect on male or female alligators. Among the herbicides tested, atrazine induced GAM aromatase activity in male hatchling alligators that was neither characteristic of males nor females, although testicular differentiation was not altered. Exposure to 2,4-dichlorophenoxyacetic acid had no effect on the endocrine parameters that were measured. Together, these studies show that exposure to some environmental chemicals (such as atrazine) can alter steroidogenesis in alligators, but the endocrine alterations previously noted for Lake Apopka, Florida, alligators can not be fully explained by this mechanism.