Coronary angiography (CA) is followed by an iodine load of 15 to 20 mg for the thyroid and may be the cause of iodine-induced hyperthyroidism. 60 consecutive patients hospitalized for CA without any thyroid history were examined and 56 had thyroid diseases with normal thyroid function. 33 patients still showed a significant decrease of 20 min Technetium uptake (TcU) and an increase of urine iodine excretion because of iodine excess 12 weeks after CA. 3 patients developed latent hyperthyroidism. 27 patients received medication of 1 g natrium-perchlorate and 60 mg methimazole 24 hours before and on the day of CA. These patients showed normal TcU and urine iodine excretion 4 and 12 weeks after CA. 1 out of these 27 patients developed overt hyperthyroidism but had PTCA without premedication 2 weeks after CA. Since Iodine excess leads to iodine-induced hyperthyroidism even in euthyroids a prophylaxis with perchlorate and methimazole is generally recommended in patients with CA.