The influence of immobilized streptokinase-streptodecase preparation on the rate of gluconeogenesis in perfused liver of normal and infarcted rats was studied. The preparations were administered in a single dose on the basis of estimated appropriate clinical dosage. It was shown that perfused liver of normal rats can produce glucose from endogenous non-carbohydrate compounds. Polysaccharide dextran carrier, a streptodecase component, leads to the growth of glucose quantity in the perfusate. At the same time, streptokinase and streptodecase suppress sufficiently the rate of gluconeogenesis in normal and infarcted rats. The streptodecase effect is particularly marked and may be connected with the inhibition of endogenous substrate induction of glucogenesis as well as the inhibition of key enzymes. Catabolic activity of streptodecase appears to be weaker than that of streptokinase. It is supposed that streptodecase may be used for the treatment of various other pathologic states apart from myocardial infarction.