1. This study has evaluated the effect of somatostatin (0.1 or 3 μg/ml) on the release of thyroxine, 3,5,3′-tri-iodothyronine and 3,3′,5′-tri-iodothyronine from perfused thyroid lobes.
2. Somatostatin did not affect either the total release of iodothyronines or the ratio between various iodothyronines in thyroid effluent from unstimulated and thyrotrophic hormone stimulated thyroid lobes.
3. The results lend no support to the idea that somatostatin present in the parafollicular cells of the thyroid should have regulatory function on thyroidal secretion of iodothyronines.