Objective To investigate the mechanisms of TSH-suppressing therapy using T4 on differentiated thyroid cancer. We evaluated the effection of the cells of pappillary carcinoma to bovine TSH and norepinephrine in vitrol. Methods The five samples of thyroid papillary carcinomas verified by frozen sections were cut off from the patients with thyroid cancer. They were dispersed by collagenase Ⅰ and trypsin and cultured in bottles, then the carcinoma cells were seeded in 96-well cell culture plates at 37℃ in 5%CO\-2 and 95%humidity for 72 h. The cells in the wells were separately stimulated with different doses of bovine TSH and norepinephrine. Results The thyroid cancer cells did not respond to bovine TSH, but were in response to norepinephrine which enhanced the proliferation of thyroid cancer cells. Conclusion The mechanisms of suppression therapy on differentiated thyroid cancer by T4 must be further investigated. Additionally, our results suggest that thyroid cancer is also under the regulation of adrenergic neurotransmitters.