Standard assay methods for saccharif ying, dextrinizing and liquefying activities of amylases are ready for practical applications in the medical field by 12 members of Nihon Iyakuyo Koso Kyokai (Society for Digestive Enzymes Manufacturers in Japan) in response to a request of the Ministry of Health and Welfare of Japan. The methods were reviewed and proposed to be adopted as standard methods in the other fields of amylase application and research . A modified Wohlgemuth's method, adapted to a continuous determination of amylase activity using an automatic analyzer for clinical purpose, was introduced for routine work . Some properties of 3 preparations of liquefying amylases of Bacillus origin, namely an ordinary type of B, subtilis (LA) and 2 thermostable types of B. subtilis (TA) and B . stearothernnophilus (StA) were examined mainly from the viewpoint of the practical applications . Thermal coefficients of the reaction rates at the early stage were in the order of decreasing StA, TA and LA, namely StA>> TA>> LA. The ratios of saccharif ying activity to liquefying activity were, LA>TA>StA. It seemed that LA cut starch into larger fragments, while StA smaller in the early stage of the reaction. The optimum temperatures under conditions for a practical liquefaction of corn starch were 95 to 100°C for TA, about 90°C for StA and about 85°C for LA . Progressive depressions in the reaction rates which were observed in the prolonged liquefying process of corn starch were, StA>LA>TA, and the liberated glucose on the DE (dextrose equivalent) basis in these processes were, LA >TA>StA.