Thyroxine by displacement analysis (T4D) along with the resin-T3 (RT3) and resin-T4 (RT4) ratios were determined analytically on serum samples from 160 ‘normal’, 50 hypothyroid and 70 hyperthyroid persons. From these data, the mathematical products of the T4D and either the RT3 or RT4 ratios were calculated and then designated the free thyroxine indices (FTI-T3 and FTI-T4). These were compared to the mean value ± 3 SD range derived from 137 normal blood bank samples. The T4D used alone was the single most accurate diagnostic parameter. The RT3 and RT4 were singularly poor tests for discriminating thyroidal dysfunction from normal. Despite theoretic considerations, the FTI-T4 was superior in diagnostic discrimination compared to the FTI-T3 with 93.8% ‘normal’ but only 16.0% hypothyroid and 0.0% hyperthyroid values in the normal range. The FTI-T4 showed a linear correlation with the free thyroxine concentration obtained by equilibrium dialysis. The FTΓ-T4 is particularly advantageous for clinical use since it is derived from the T4D which obviates interferences from iodine contamination and the RT4 which can be performed in concert with the T4D by a unified procedure.

Successful treatment of hyperthyroidism is predicated upon an understanding of the pharmacology of antithyroid drugs as well as upon a knowledge of their effects on pathways of thyroidal iodide metabolism. Research into the relationship between chemical structure and biologic action of numerous antithyroid compounds has served as a basis for their classification and for selection of those of greatest potency for clinical trial. Biochemical determination of the site and mode of action of compounds affecting thyroid hormonogenesis, although incomplete, allows a tentative working hypothesis which must be periodically revised as further evidence is accumulated. During the 17 years since the introduction of thiouracil, clinical pharmacologic investigations have established optimal dosage schedules, the incidence of toxic reactions, and the indications for the effective use of these drugs. Such studies have further served to develop programs for the management of patients with hyperthyroidism with special emphasis on the use of antithyroid compounds in long‐term therapy, preoperative preparation, and use during childhood or pregnancy. Although refinements in surgical approach and the general availability of radioactive iodine have necessitated modifications in the indications for their use, antithyroid drugs still maintain a secure position as therapeutic agents in the treatment of hyperthyroidism.