Thyrotropin (TSH) receptor is the main autoantigen and the target of thyroid-stimulating antibodies in Graves' disease. In the present studies, in order to shed further light on the role of TSH receptor in thyroid autoimmune disease, we investigated the effects of TSH receptor blockade on functional and immunological responses to thyroid stimulation by Graves' immunoglobulins in the nude mouse bearing human thyroid transplants. Injecting the nude mice with purified Graves' immunoglobulins G resulted in a dose-dependent stimulation of thyroid hormone production, an inducement of cellular hypertrophy of transplant thyrocytes, and an expression of the HLA-DR antigen by up to 75% of the transplant thyroid follicular cells. Treatment of the animals with the TSH receptor antagonist asialoagalacto-hCG was able to inhibit the stimulation by Graves' immunoglobulins G of thyroxine production, cellular hypertrophy of transplant thyrocytes, and HLA-DR expression by thyroid follicular cells in the human transplants. The present data provide direct evidence for an involvement of the human TSH receptor in mediating both the functional disturbance (hyperthyroidism) and the immunological disorder in Graves' disease and add further support to the concept of using TSH receptor antagonists in the management of the disease.