The RTH syndrome is an instructive example of a receptor resistance syndrome. A typical case history is reported here. The patient had had symptoms for many years and was first diagnosed as having inappropriate secretion of TSH. Pituitary tumour was excluded. The primary symptom was palpitations and the patient was partially thyroidectomized many years ago on suspicion of thyrotoxicosis. She was then given substitutional Eltroxin, but, because of palpitations, the dose was reduced to almost zero, after which the patient contracted symptoms suggesting myxoedema. The thyroid values could not be used for clinical assessment, however the symptoms of myxoedema disappeared when the Eltroxin dose was increased to 75 micrograms/day. When the dose was increased further the heart symptoms became too troublesome. The patient had no signs of underlying heart disease.