SummaryTwo cases of chronic 3, 5, 3’-triiodo-thyroacetic acid (Triac) consumption (2.1 mg/day) are reported. Profound alterations of thyroid function were observed: thyroxine and free thyroxine concentrations were low, normal to excessively high triiodothyronine values were detected and thyroid stimulating hormone response to 200figthyroid releasing hormone i.v. was abolished.The literature concerning Triac use is reviewed, and the efficiency of the drug in the treatment of obesity is discussed.