 chemicals having a capacity to disturb the endocrine system have attracted considerable interest during recent years . 
 there is a shortage of well - characterized in vivo tests with which to study such disturbances in different classes of vertebrates . in the present study , 
 test end points related to reproduction in the japanese quail were used to examine the estrogenic activity of chemicals . 
 the synthetic estrogens ethinylestradiol ( ee(2 ) ) and diethylstilbestrol ( des ) , used as model compounds , were injected into the yolk of embryonated eggs . 
 after the birds had been raised to sexual maturity , we examined sexual behavior , plasma testosterone concentrations , and testis morphology in adult males . 
 the lowest doses resulting in a significantly depressed male sexual behavior were 6 ng / g egg for ee(2 ) and 19 ng / g egg for des . 
 testis weight asymmetry was increased at 6 ng ee(2)/g egg , but des had no effect at any treatment level . 
 the area of the androgen - dependent cloacal gland was significantly reduced at 57 ng des / g egg . 
 no effects on plasma testosterone concentration or body weight following exposure to ee(2 ) or des were observed at any dose level . 
 depressed male sexual behavior was the most sensitive of the end points studied , and we suggest that this ecologically relevant end point be included in avian in vivo testing for neuroendocrine disruptors.imagesfigure 1figure 2 
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