Many xenobiotic compounds introduced into the environment by human activity have been shown to adversely affect wildlife. Reproductive disorders in wildlife include altered fertility, reduced viability of offspring, impaired hormone secretion or activity and modified reproductive anatomy. It has been hypothesized that many of these alterations in reproductive function are due to the endocrine disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo. Thus, a disruption of the normal hormonal signals can permanently modify the organization and future function of the reproductive system. We have examined the reproductive and developmental endocrinology of several populations of American alligator (Alligator mississippiensis) living in contaminated and reference lakes and used this species as a sentinel species in field studies. We have observed that neonatal and juvenile alligators living in pesticide-contaminated lakes have altered plasma hormone concentrations, reproductive tract anatomy and hepatic functioning. Experimental studies exposing developing embryos to various persistent and nonpersistent pesticides, have produced alterations in gonadal steroidogenesis, secondary sex characteristics and gonadal anatomy. These experimental studies have begun to provide the causal relationships between embryonic pesticide exposure and reproductive abnormalities that have been lacking in pure field studies of wild populations. An understanding of the developmental consequences of endocrine disruption in wildlife can lead to new indicators of exposure and a better understanding of the most sensitive life stages and the consequences of exposure during these periods.