Known since 1967 and usually familial, the syndrome of tissue resistance to thyroid hormones may take one of two different forms, depending on the receptors involved. When resistance affects both peripheral and pituitary receptors, plasma thyroid hormone levels are high despite the lack of thyrotoxicosis, thyroxine and triiodothyronine are ineffective, even in high dosage, and plasma TSH increases to explode under TRH. When resistance only affects pituitary receptors, there is moderate thyrotoxicosis with paradoxical and inappropriate TSH increase. Contrary to expectations, nuclear receptors to triiodothyronine are perturbed in only a few cases. Reduction of thyrotropic hyperfunction, which is the primary purpose of treatment, can be achieved with D-forms of thyroid hormones or with somatostatin and its derivatives.