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The hydrolysis of ethyl (R)-2-(benzyloxycarbonylamino)-3-sulfamoylpropionate (blocked cysteic acid S-amide) by native and immobilized alpha-chymotrypsin was studied. The experiments were performed using a constant enzyme/substrate ratio of 1:8 and at a temperature of 10-40 degrees C; the immobilized enzyme was bound to a dialdehyde cellulose matrix. A kinetic equation (Eq.10) was found to be applicable which confirms that the mechanism of the enzyme reaction consists of several stages, irrespective of the enzyme state. The temperature dependence of the reaction velocity was investigated and applied using the Arrhenius equation. The constant value thus obtained for the activating energy showed that the active centres retained their character during immobilization. The differences between the velocities of the reaction with immobilized and with native enzyme corresponded to the different number of active centres during the reaction time. Based on these results a kinetic model of the mechanism of the studied reaction is presented which includes an initial balanced stage of the chemosorption type.