The influence of three thiol compounds: beta-mercaptoethylamine thioglycolic acid and thioacetic acid on the urease-catalyzed hydrolysis of urea was studied. The reaction was carried out in phosphate buffer pH 7.0 at 25 degrees C The progress of the reaction was observed by means of a calorimetric method using an isoperibol calorimeter. The total reaction progress curves, Delta T vs. t, were interpreted with the help of the integration Jennings-Niemann method and the inhibition constants were calculated.