SUMMARY Serum concentrations of triiodothyronine (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) have been measured in subjects from an endemic goitrous area of New Guinea. An increase in TSH concentration and a decrease in T4 concentration was found in both goitrous and non‐goitrous subjects, both abnormalities being more frequent in the goitrous group. In the majority of subjects (93%) the T3 level fell within the normal range. Euthyroidism appears to be preserved in the iodine deficient state by the continued production of normal amounts of T3, the intrinsic metabolic activity of T4 being relatively unimportant.

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SUMMARY The thyroidal component of the response to thyrotrophin releasing hormone (TRH) has been studied by measurement of serum triiodothyronine (T3) and thyroxine (T4). In normal subjects a significant increase in serum T3 followed intravenous administration of TRH 200 μg. A less consistent increase was detected in serum T4 concentration. Oral TRH at a dose of 40 mg caused a significant rise in serum T4 in normal subjects. The increase in T4 at 24 hr was considered to provide a convenient index of pituitary and thyroidal response. Fourteen patients with pituitary disease, of whom twelve were euthyroid, were investigated by an oral TRH test. The majority of these patients retain a normal pituitary TSH reserve though a small group can be identified in whom it is diminished. A significant correlation was obtained between the T4 and TSH response to oral TRH. It is suggested that measurement of serum concentration of thyroid hormone is of value in the assessment of the pituitary response to TRH and the integrity of the pituitary‐thyroid axis.

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