An empirical equation for representing the course of the reaction has been developed for amylase ofAspergillus oryzae by using the method of time value estimation as a measure of enzyme activity. A convenient form of the equation for calculating and plotting results is t/x=bt+a/(E), where t=reaction time, x=amount of reaction products formed, (E)=enzyme concentration, a/(E)=reciprocal of initial velocity. The parameter b makes the equation of a rather universal applicability over large portions of the reaction curves. If b=0, the reaction is of zero order; if b=1/(S)o, the reaction is of second order; a first order reaction can be represented over a range from 0 to 55% if b≏1/2(S)o. In the case of aMichaelis-Menten mechanism, b=Ks/2(S)o[(S)o+Ks] afterBrant andAlberty (1961, personal communication), and then the ratio of (S)o/Ks limits the range of validity of the empirical equation. As a tool for determining enzyme activity over a wide range of reaction, the equation is most useful in cases where the rate of reaction decreases rapidly,e.g. if (S)o/Ks is small, or if inactivation and/or inhibition of the enzyme during the reaction is involved. For the assay of enzymes the main advantages of the empirical equation over the integratedMichaelis-Menten equation, and other more complicated variations thereof, are ease of handling and applicability to a large number of enzymes.