The findings of the study suggest that (1) thyrotoxicosis stimulates the oxidative stress response and the production of inflammatory cytokines (IL-10 and TNF-alpha), (2) there is a relationship between oxidative stress parameters and inflammatory cytokines, (3) melatonin prevents the increase in FT3 and FT4 caused by chronic T4 injection, and (4) melatonin-based antioxidative treatment inhibits thyroid hormone induced increases in MDA, GSH, NO•, and TNF-alpha levels. Here, TNF is linked to thyrotoxicosis.