Résumé : Induction of cell proliferation by mitogen or growth factor stimulation leads to the specific stimulation or repression of a large number of genes. To better understand differentiated epithelial cell growth regulation, we have initiated a study to identify genes which are regulated by the thyrotropin-dependent mitogenic pathway in dog thyroid cells. A thyroid cDNA library was prepared from a methimazole and propylthiouracil-treated dog and differentially screened with probes derived from control or stimulated thyroids. Among 19 clones isolated, 6 encode known proteins (inwardly rectifying potassium channel, nucleosome assembly protein, ribosomal protein L7, elongation factor 1alpha, non-muscle myosin light chain, and heat shock protein 90beta). The 13 others correspond to proteins whose function is unknown. Among them, 5 correspond to mRNAs whose expression was modulated by mitogenic stimulation of thyrocytes in primary culture. A preliminary characterization of two of these cDNAs is reported: clone 5, which might represent a novel, atypical protein kinase, and clone 3, which contains ankyrin-like repeats, suggesting that it might interact with other proteins.