To investigate the influence of chronic ethanol consumption on circulating thyroid hormone levels, male and female rats were given 20% ethanol as the only drinking solution daily for 8 weeks. Blood ethanol levels ranged 30–45 mg/L. In male rats serum T 4 decreased from the initial mean ± SD value of 5.2±1.4 to3.0 ±0.7 μg/dl; T 3 decreased from initial value of 97±14 to 66±11 ng/dl and rT 3 decreased from initial value of 19±9 to 10±1 ng/dl after 8 weeks of ethanol ingestion. Under similar experimental conditions, female rats showed a significant decrease in serum T 4 and rT 3 levels; however, T 3 levels decreased slightly but not significantly as compared to initial values. The results indicate adverse effect of chronic ethanol intake on serum thyroid hormone levels in rats.