Rats were intoxicated with mercuric chloride (1mg/kg b.w.) daily, for 12 weeks. A decrease in total glycosaminoglycan content was shown in the skin, the lungs, the liver and the heart muscle. These changes were accompanied by a slight alteration of the glycosaminoglycan pattern, a decrease in hyaluronic acid in the skin, the lungs and the heart muscle and an enhancement of heparan sulphate level in the kidneys. In serum of mercury-intoxicated rats, an increase in total glycosaminoglycan levels was shown. This enhancement was caused by elevation of almost all fractions. Urine output of glycosaminoglycans was higher in mercury-treated animals as compared to the controls.