Résumé : A bout of hyperthyroidism with ophthalmopathy was followed by the development of a cervical polymicroadenopathy, lymphocytosis and a progressive depression of immunoglobulins. The thyro thymic lymphatic migration was accelerated. Under neomercazol treatment, the modified thyroproteins which are brought to the thymus seemed to exercise an efficient tolerogenic influence. The paracortical zones, 'thymodependent', of the lymphoid nodules were colonized by a particular population of T lymphocytes. Antibody producing plasmatocytes were not detected. The increase of the thyroid contribution and its qualitative modifications mobilized homeostatic axis thyroid thymus lymphoid nodules, whose adjusted tolerogenic power appeared to condition the utilization of thyroid products for physiological and metabolic purposes.