A rapid method for analysing enzyme-substrate interactions using a discriminant analysis program is described. This technique identifies the structural features of substrate molecules which are important in determining metabolic activity. Two model systems, nucleoside diphosphatase activity of Golgi membranes and the interaction of yeast hexokinase with a range of D-sugars, are used as illustrations of the technique. The conclusions from both models are consistent with those previously obtained from analytical techniques.