Urease-catalyzed hydrolysis of urea was studied in the absence, and presence, of 0.3 and 0.8 mmol dm(-3) 2-mercaptoethanol in phosphate buffer at pH 7.0 at 25 degrees C with the use of an isoperibol calorimeter. The extent of reaction with time, Delta T vs. t, was interpreted with the help of the integrated Michaelis-Menten equation, and the inhibition constant K-i was obtained from linear transformations of the equation (Jennings-Niemann, Yun-Suelter and Booman-Niemann). The obtained value of K-i was equal to 0.87+/-0.10 mmol dm(-3).