It is shown that a number of workers have incorrectly considered that the rate of decline (regression) of induced liver enzyme activity is directly proportional to the actual enzyme concentration whereas both theory and observation indicate that the decay curve is a function of both a first-order degradation rate and a counteracting zero-order normal rate of synthesis. Thus, semilogarithmic plots of actual enzyme concentration as a function of time during regression have resulted in the appearance in the literature of spuriously high values for the half-lives of several enzymes and/or erroneously low values for their degradation rate constants. Since these constants are a major factor in the analysis of enzyme induction kinetics, the accuracy of their determination from activity regression data is extremely important. The correct method for treating such data is reiterated.