At the Annual Meeting of this Association held at Belfast last July, Sir Frederick Mott gave you an address on the thyroid gland and promised a further contribution with regard to the iodine content. This paper is an attempt to correlate the iodine content with histological structure and with the mental and bodily condition of the patient. I must apologize for the work being far from complete, as most of the time since then has been taken up with the examination of the published methods for the estimation of iodine in the gland, and owing to certain objections to these methods it has been necessary to invent a process without these objections, and which, at the same time, is carried out with a minimum expenditure of time and material.