In 31 patients with acute myocardial infarction triiodothyronine (T3), free triiodothyronine (FT3), thyroxine (T4), free thyroxine (FT4), thyrotropin (TSH) and TBG were measured and T3-test was performed on the 1st and the 10th day of hospitalization. The 1st day values for T3, FT3 and TBG were significantly lower, and T4 and TSH were significantly higher than in the control group. The same differences were noted on the 10th day for T3, FT3 i T4. TBG was significantly higher than the 1st day. TSH was lower and it was not significantly different from control values. These results are compatible with clinical observations described in severe nonthyroidal illnesses.