The relationship between blood pressure and hyperthyroidism is significant if some views of the present day are true. It is common knowledge that there is an increased pulse pressure in hyperthyroidism. Statements have been made that if this were continued over a sufficient time, cardiovascular changes and permanent arterial hypertension might ensue. Furthermore, it is the belief of some writers that the nontoxic adenomatous goiter can lead to similar changes over a period of years. There has been no adequate survey, as far as I am aware, to show that either active hyperthyroidism or prolonged but slight over-activity of the thyroid in otherwise clinically nontoxic goiter leads to permanent cardiovascular degeneration, hypertension or cardiac enlargement. In observing patients who have been operated on for toxic goiter, one frequently finds the blood pressure higher after operation than before, although the basal metabolic rate is normal and the patient is clinically free