Oxidative stress plays a role in the pathogenesis of many chronic diseases. It is recognized in overt hypothyroidism while its existence in subclinical hypothyroidism (SCH) is not well established. The aim of this study was to determine whether there was increased oxidation of lipids and proteins in SCH, and examine their association with lipids and thyroid hormones. Methods: Male adults (35-59 years) with SCH (n=467) and euthyroid controls (n=190) were studied. Anthropometric measurements, plasma lipids, thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), total antioxidant capacity (T-AOC), lipid peroxidation products, malondialdehyde (MDA), advanced oxidation protein products (AOPP) and dityrosine concentrations were measured. Results: Plasma concentrations of MDA were significantly higher (p<0.05) in SCH (8.11±1.39 nmol/mL) compared with euthyroid controls (7.34±1.31 nmol/mL) while AOPP, dityrosine and T-AOC levels were not different. MDA was not associated with TSH (β=-0.019, P=0.759), FT4 (β=-0.062, P=0.323) and FT3 (β=-0.018, P=0.780) in SCH while levels increased with elevated total cholesterol (β=0.229, P=0.001), LDL (β=0.203, P=0.009) and triglycerides (β=0.159, P=0.036) after adjustment for ageand body mass index. T-AOC reduced (β=-0.327, P=0.030) with increased MDA in euthyroid controls and not in SCH (β=-0.068, P=0.349), while levels increased with elevated triglycerides in both groups. Conclusion: Oxidative stress was increased in subclinical hypothyroidism as evidenced by the elevated lipid peroxidation product, malondialdehyde, while protein oxidation was absent. Thus, reduction of oxidative stress may be beneficial in patients with subclinical hypothyroidism Uvod: Oksidativni stres učestvuje u patogenezi mnogih hroničnih oboljenja. Ima ulogu u manifestnoj hipotireozi, dok njegovo prisustvo u subkliničkoj hipotireozi (SH) nije sasvim razjašnjeno. Cilj ove studije bio je da se odredi da li postoji povišena oksidacija lipida i proteina u SH i da se istraži njihova povezanost sa lipidima i tireoidnim hormonima. Metode: Ispitivani su odrasli muškarci (35-59 godina) sa SH (n=467) i eutireoidne kontrolne osobe (n=190). Izmereni su antropometrijski parametri, koncentracije lipida u plazmi, tireostimulišućeg hormona (TSH), slobodnog tiro- ksina (FT4), slobodnog trijodtironina (FT3), ukupni antioksidantni kapacitet (T-AOC), proizvodi lipidne peroksidacije, malondialdehid (MDA), uznapredovali proizvodi proteinske oksidacije (AOPP) i ditirozin. Rezultati: Koncentracije MDA u plazmi bile su značajno povisene (p<0,05) u SH (8,11 ±1,39 nmol/mL) u poredenju sa eutireoidnim kontrolnim osobama (7,34±1,31 nmol/mL) dok se nivoi AOPFJ ditirozina i T-AOC nisu raz- likovali. MDA nije bio povezan sa TSH (p =-0,019, P=0,759), FT4(p=-0,062, P=0,323) i FT3 (p=-0,018, P=0,780) u SH dok su nivoi rasli s povisenim vrednostima ukupnog holesterola (p = 0,229, P=0,001), LDL(p = 0,203, P= 0,009) i triglicerida (P = 0,159, P= 0,036) posle prila-gocfavanja za starost i indeks telesne mase. Porast nivoa MDA bio je pracen snizenjem nivoa T-AOC (P=-0,327, P=0,030) kod eutireoidnih kontrolnih osoba, ali ne i u SH (P=-0,068, P=0,349), dok su u obe grupe nivoi rasli s porastom triglicerida. Zaključak: Oksidativni stres bio je povišen u subkliničkoj hipotireozi, što su pokazali i povišeni nivoi proizvoda lipidne peroksidacije, malondialdehida, dok je oksidacija proteina bila odsutna. Stoga, snižavanje oksidativnog stresa može biti korisno kod pacijenata sa subkliničkom hipotireozom