Abstract: The object of the invention is to provide a reagent for quantitatively determining creatine kinase with improved storability in liquid form as well as a method for quantitatively determining creatine kinase with stable measurements. Disclosed are a method for quantitatively determining creatine kinase, which comprises activating creatine kinase in a sample in an aqueous medium in coexistence with a trivalent phosphorus compound and a sulfhydryl-containing compound and then determining creatine kinase activity; a method for stabilizing a sulfhydryl-containing compound, which comprises allowing a trivalent phosphorus compound to coexist with a sulfhydryl-containing compound; and a reagent for quantitatively determining creatine kinase, which comprises a trivalent phosphorus compound, a sulfhydryl-containing compound, and a reaction substrate for creatine kinase.

Abstract: Disclosed is a method for stably storing a liquid diagnostic reagent, comprising air-hermetically keeping the liquid diagnostic reagent in a closed container in the presence of a disoxidant therein. Preferably, at least one of the liquid diagnostic reagent and the disoxidant is covered with a separating container made of a material pervious to oxygen but not to solutions. The liquid diagnostic reagent may comprise an enzyme or an indicator.

Abstract: Glucose 6-phosphate dehydrogenase is stabilized in a clinical assay reagent with at least one stabilizer selected from among hydroxylamines, aldehyde scavengers dimethylthiocarbamoyl chloride, 2-(2-aminoethylamine) ethanol, and their salts. The reagent may be in liquid or lyophilized form.