The case histories of three patients with hyperthyroidism due to overproduction of thyroid-stimulating hormone (TSH) by the pituitary gland are described. In the first patient treatment with the T3-metabolite 3,5,3'-triiodothyroacetic acid (TRIAC) led to complete clinical and biochemical normalization. In the second patient treatment with the dopaminergic agonist bromocriptine led to a temporal amelioration of hyperthyroidism. In the third patient, who was the only one with a proven pituitary adenoma, hypersecretion of TSH could be controlled by administration of the somatostatin analogue octreotide. It is emphasized that patients with this disorder should preferably not be treated with thyrostatic drugs, radioactive iodine or thyroid surgery. The success rate of these treatment modalities is lower than normal, they may lead to an increase of goiter size, and they potentially may promote growth or development of a TSH-producing adenoma. Treatment should be aimed at diminishing TSH hypersecretion.