Thyroid hormones or methylthiouracil (MTU) were given to healthy rats or animals with hepatic fibrosis. Administration of thyroid hormones to rats with carbon tetrachloride-induced hepatic fibrosis caused an increase in serum activity of matrix-degrading hydrolases although the increase was lower than that in healthy animals treated with thyroid hormones only. Methylthiouracil administration had no effect on the enzyme activity in healthy rats and resulted in a decreased activity in rats with hepatic fibrosis.