Resistance of the pituitary gland to thyroid hormones.

Inappropriate secretion of TSH (assayed using an immunoradiometric method) due to resistance of the pituitary to thyroid hormones is described. The pa tients present with thyrotoxicosis. Total T3 and T4 levels (by radioimmunol ogical assays) are high, and clinical manifestations are present in all tar get organs except the anterior pituitary, which is apparently insensitive t o physiological feedback, This suggests that thyroid hormone receptors in t he anterior pituitary and/or brain may be different in distribution or, mor e likely, in structure from those in other target organs.