Groups of rats were fed a low iodine diet, or the same diet supplemented with known amounts of iodine. About 2–3 weeks later radioiodine (*I) was injected and the rats were killed on the next day or at different daily intervals after »blocking« with KClO4 and withdrawal of I supplements. Most of the animals had normal thyroid weights and plasma PBI. A few groups of rats were in a mildly iodine deficient state. The patterns of *I and 127I distribution among thyroidal iodine containing compounds was determined. It was found that these patterns were not the same in all thyroids with normal weights. Thus the pattern changed slightly but gradually concomitantly with the iodine intake and/or the thyroidal iodine content: The M*IT/D*IT2)3), MIT/DIT and T3*/T4* ratios decreased as the iodine intake and/or thyroidal iodine content increased. A decrease in the thyroidal I stores after pre-labelling of the thyroidal I-containing compounds also resulted in the same changes in the *I distribution pattern. Normal thyroids containing the same amount of iodine have similar iodoamino acid composition. The present data show that the iodoamino acid composition of the normal thyroid is affected by the availability of iodine, though to a lesser degree than that of I-deficient glands.