Here we report the generation of transgenic mice lines expressing the RET/PTC1 oncogene under the control of the thyroid-specific rat thyroglobulin promoter.     ///    Development of thyroid papillary carcinomas secondary to tissue-specific expression of the RET/PTC1 oncogene in transgenic mice..     ///    RET/PTC1-transgenic mice developed thyroid tumors displaying the histological aspect of papillary carcinomas.     ///    These arrangements cause the fusion of the tyrosine-kinase domain of RET to the 5'-terminal region of different genes creating the RET/PTC chimeric oncogenes. 