A procedure to obtain the overall rate of hydrolysis of biopolymers is proposed, based on the fitting of the experimental data x = f(t) to cubic spline functions and from these, by differentiation, to obtain dx/dt. The values of these dx/dt slopes are an exclusive function of the conversion, x, when E(0), S-0, pH and temperature are constant. The fitting of dx/dt versus x leads to equations of the type dx/dt = a . x exp(-b . x) for the glucoamylase-starch system, where b = 8.75 and a = f(E(0), T).