Estrone sulfate (E+ S) is predominantly present in the maternal circulation of pregnant animals and is excreted into the feces and urine. Hence, it is estimated that E+ S is partly present in the environment, which may be discharged from farms. The present study was undertaken to examine whether E+ S a#ected the endocrine function in animals. Male Japanese quails were intramuscularly treated +mg of E+ S everyday for . days. Blood samples were obtained just before the treatment and at the . days

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... after the onset of treatment to measure the concentrations of testosterone, E+ S and triacylglyceride. Apoptotic cell death was detected in the para$n sections of testis. The weight of testis was significantly reduced in the E+ S treated groups compared with that of untreated group. Treatment of E+ S to the quail significantly increased plasma E+ S and triacylglyceride concentrations and significantly reduced plasma testosterone concentration. Some Sertoli cells in the E+ S treated group showed apoptotic cell death, whereas there is few apoptotic cells in the untreated group. These results indicate that E+ S has ability to induce apoptosis in the testicular cells and reduction of testicular weight and testosterone concentration, possibly due to the unconjugation of E+ S. It is also suggested that E+ S may be one of risk factors for endocrine disrupter in wild life.