Many enzymatic reactions yield volatile products either directly or by cascade sequences, so it seems possible that head-space chromatography might be used to determine enzymatic activity. The activity of urinary kallikrein, as arginine esterase, has been determined in this way by using the N(alpha)-acetyl-L-phenylalanyl-L-arginine ethyl ester as substrate and measuring the ethanol yielded on incubation for 10 min at 30 degrees, followed by quenching of the reaction. The method has been applied to aqueous solutions and urine.