ABSTRACT            
This study aimed to evaluate changes in plasma malondialdehyde, total thiol concentration and total anti-oxidant activity in newly diagnosed Graves' disease and toxic multinodu-lar goiter patients prior to antithyroid treatment and after restoration of stable euthyroid state.
Forty subjects were included in this study. Thirty patients with hyper-thyroidism, which were classified into two groups, the first (group I) Com­prised 15 patients with hyperthyroi-dism due to untreated Graves' dis­ease, and the second (group II) Comprised 15 patients with hyperthyr-oidism due to untreated toxic multi-nodular goiter. Ten patients of each group were treated pharmacologically
with antithyroid drug carbimazol (30
mg/day for 8 weeks). Total thyroxin (T₄), total triiodothyronine (13), TSH, malondialdehyde, total thiol concen­tration and total antioxidant activity were estimated before initiation of treatment. After apparent attainment of euthyroid state, all tests were re­peated for ten of the patients with Graves' disease and ten of the pa­tients with toxic multinodular goiter.
The results of this study revealed that there were a statistically highly significant increase in plasma malan-dialdehyde (MDA), a significant de­crease in plasma thiol and very highly significant decrease in total antioxi­dant activity in both patient groups when compared to healthy controls. After treatment, plasma MDA levels