A computer approximation with polynomial quotients was used to evaluate from experimental data the dependence of the initial velocity of D-glyceraldehyde-3-phosphate dehydrogenase reaction on the concentration of substrates. The initial velocity values were determined at optimum conditions, over a wide range of substrate concentrations and by interpolating the time curve of enzyme reaction as t leads to 0. A further computer approximation with polynomial quotients, without any implied hypothese, gave the best fit to the experimental results. The analysis of this final equation shows that two types of catalytic sites may exist. Due to the complexity of the system, the results are compatible either with the ordered binding or with rapid equilibrium random binding of substrates to each separate, but interacting type of sites. Previous experimental data showing the formation of abortive and dead-end complexes can be interpreted as kinetic effects, inherent in the mechanism. Results at variance with earlier data can be explained by the different experimental conditions.