The effects of iodides and other halides given with thiouracil.

1. Concurrent administration of iodide and thiouracil or propylthiouracil for two to six weeks results in thyroid glands which are 20 to 30 per cent lighter than those produced by the administration of thiouracil or propylthiouracil alone. 2. Iodide does not decrease the effectiveness of the goitrogenic drugs in lowering the metabolic rate. Consequently, its antigoitrogenic action cannot be attributed to an increase in the supply of available thyroid hormone. 3. The thyroid follicles of the rats receiving iodide with thiouracil contain more colloid and show less hyperplasia. The effect of the iodide seems to be best described as antithyrotropic in some sense.