A number of environmental contaminants have been shown to interfere with the endocrine system. Many of these compounds bind to estrogen receptors, thereby potentially disrupting estrogen-regulated functions. In this paper, we review some background data on avian sexual differentiation and present some of the results from our studies on effects of estrogenic chemicals administered during sexual differentiation in the Japanese quail. Initially, our goal was to elucidate whether a decreased male sexual behavior in quail is a suitable endpoint for studying long-term effects of exposure to estrogenic compounds during sexual differentiation in ovo. We thereafter tested some environmental pollutants, suspected to act via mimicking estrogens, using the test system developed. Results from our studies on the synthetic estrogens ethinylestradiol and diethylstilbestrol, as well as the environmental pollutants bisphenol A, tetrabromobisphenol A, and o,p'-DDT are reviewed in this paper. We conclude that the Japanese quail is well suited as an animal model for studying various long-term effects after embryonic exposure to estrogenic compounds. Depressed sexual behavior proved to be the most sensitive of the variables studied in males and we find this endpoint appropriate for studying effects of endocrine modulating chemicals in the adult quail following embryonic exposure.