Sodium pentosan polysulphate is a polymer of beta-D-xylopyranose which possesses some of the biological properties of the endogenous acid polysaccharides such as heparin. The actions of this compound on plasma lipids, carbohydrate metabolism and fibrinolysis have been studied using the human forearm technique. Ten healthy volunteers were investigated in the fasting state, and blood flow measurements and blood samples were taken before and at 60 and 90 minutes after 100 mg sodium pentosan polysulphate by intramuscular injection. Following administration of the drug, significant changes occurred in plasma triglyceride, free fatty acid (ffa) and glycerol levels. Triglycerides fell (P less than 0,001) and glycerol and FFA rose (P less than 0,001. Changes were largely owing to activation of intravascular lipolysis, although an effect on stored triglycerides was also noted. Fibrinolytic activity also increased after drug administration, but no changes were noted in insulin exchange or glucose metabolism.