We have developed mouse models for tumors affecting the epithelial cellular compartment of the thyroid which has been targeted using the bovine thyroglobulin (bTg) promoter. Transgenic mice expressing the human activated c-Ha-Ras gene developed papillary thyroid carcinomas demonstrating the oncogenic potential of activated Ras gene in the thyroid gland. Transgenic mice express the mutant form of the a subunit of the adenylate cyclase-coupled G alpha(s) with mutations at codon 201 (R201H). The expression of this mutant transgene is not by itself sufficient to produce benign tumors or even hyperplasia, but the transgenic mice have inherited a predisposition to develop thyroid adenomas.