The action of pig pancreas α‐amylase on various samples of hydroxyethyl starches (HES) has been studied. It has been shown that the hydrolysis rates of both 2‐hydroxyethyl starches (2‐HES) and 6‐hydroxyethyl starches (6‐HES) decreased as M. S. or D. S. increased, i. e. the more the unsubstituted anhydroglucose residues the specimen contained, the more rapidly the degradation took place. Further evidences have been obtained indicating that 2‐O‐hydroxyethylanhydroglucose residues played a more significant role on the resistance to α‐amylase action than 6‐O‐hydroxyethyl‐anhydroglucose residues. Thus, each sample of 2‐HES has been more resistant to α‐amylolytic attack than the corresponding specimen of 6‐HES, regardless of the same content of unsubstituted anhydroglucose residues.

The blood concentration, renal excretion, and molecular‐size distribution of 6‐O‐hydroxyethyl starch (6‐O‐HES) and 2‐O‐hydroxyethyl starch (2‐O‐HES), which were infused into rabbits, were compared. As a result, 6‐O‐HES showed a more rapid elimination from the body than 2‐O‐HES did, thus indicating that 6‐O‐HES was subjected to the same metabolic changes as 2‐O‐HES was, which had a lower molar substitution of hydroxyethyl groups by 0.2 to 0.3. This result might be attributed to the substitution‐site effect of hydroxyethyl groups on the enzymic degradation of hydroxyethyl starch by α‐amylase.

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The degradation sites of hydroxyethyl starch (HES) by pig pancreas α‐amylase were determined by gas liquid chromatography. As a result, it was confirmed that HES could be hydrolyzed by α‐amylase only at the glucosidic bond of unsubstituted glucose residues, but not at the bond of 2‐0‐, 3‐0‐, and 6‐0‐hydroxyethylglucose residues. Furthermore, it was suggested that the enzymic degradation rate of HES could be well determined by measuring the reducing power.