Ž . The Science of the Total Environment 233 1999 5766 The avian egg as a test system for endocrine disrupters: effects of diethylstilbestrol and ethynylestradiol on sex organ development Cecilia Berg a,  , Krister Halldin a , Anna-Karin Fridolfsson b , Ingvar Brandt a , Bjorn Brunstrom a ¨ ¨ a Department of En ironmental Toxicology, Norby  agen 18A, S-752 36 Uppsala, Sweden ¨ b Department of Animal Breeding and Genetics, Swedish Uni  ersity of Agricultural Sciences, Uppsala Biomedical Centre, Box 597, S-751 24 Uppsala, Sweden Abstract Many environmental contaminants are known or suspected to interfere with hormonal function in animals. In vivo test methods to detect and characterize chemicals that disrupt the endocrine system are therefore urgently needed. In this study, we assessed the usefulness of abnormalities of the reproductive organs as test endpoints for estrogenic Ž . activity of xenobiotics in Japanese quail embryos. Two synthetic estrogens, diethylstilbestrol DES and ethynylestra- Ž . diol EE , were injected into the yolks of embryonated eggs. At a dose as low as 2 ng EE g egg, all male embryos 2 2 became feminized, containing ovary-like tissue in the left testis. The extent of feminization of the testes was Ž . determined by measuring the relative area of the ovary-like component. Persistent Mullerian ducts oviducts in male ¨ embryos, and malformations of the Mullerian ducts in females occurred at 2 ng EE g egg and higher doses. DES ¨ 2 was approximately one-third to one-tenth as potent as EE . The morphological changes studied were dose-depen- 2 dent, indicating that they are useful as test endpoints for estrogenic activity. Feminization of the left testis in males proved to be the most sensitive endpoint. We propose the quail egg as a simple in vivo test system for estrogenic compounds.  1999 Elsevier Science B.V. All rights reserved. Keywords: Endocrine disruption; Environmental estrogens; Reproductive organ morphology; Ovotestis; Test system; Biomarkers; Japanese quail; Ethynylestradiol; Diethylstilbestrol  Corresponding author. 0048-969799$ - see front matter  1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 8 - 9 6 9 7 99 00179-5