[en] Male Wistar rats were restricted on iodine intake by feeding pure diets, without iodine addition. The high fat diet contained 50% fat (HFD), the low fat diet 3% fat(LFD). Control animals received the same diets, but with iodine addition. After feeding the diets for 7 or 19 weeks liver deiodinase activity was estimated. The iodine deficient animals showed a diminished enzyme activity in both diet groups. But after feeding the diet without iodine addition for 7 weeks the deiodinase activity significantly decreased in the HFD-group only in relation to liver weight per 100 g body weight. After 19 weeks the liver deiodinase activity in the HFD-group was diminished significantly, but the decrease was much smaller than in the LFD-group. The estimation of relative thyroid weight and iodoamino acid distribution demonstrate that the level of iodine deficiency was in iodine restricted HFD-rats greater than in appropriate LFD-rats. This result was verified by investigations of thyroidal radio iodine uptake and iodine content, PB¹³¹I, serum iodine and T₄ levels in both diet groups. The reason for the lower decrease of deiodinase activity at higher iodine deficiency in HFD-rats as compared to LFD-rats and the possible importance of food enriched with fat in endemic goiter areas is discussed. (author)