A whole cell biocatalyst (Kluyveromyces lactis) consisting in permeabilized cells stabilized with glutaraldehyde under conditions that preserve the beta-galactosidase activity was characterized in connection with autolytic processes, cell wall effects and sensitivity to shear stress and exogenous proteases. Permeabilized cells display a typical autolytic process that was characterized by the accumulation of extracellular amino-nitrogen due to proteolysis, carbohydrate solubilization and release of enzyme activities. The stabilization of the cell system was manifested by the inhibition of the autolytic process. This phenomenon was evident by the absence of proteolysis and enzyme solubilization. Cell wall autolysis appears not to be totally blocked by the glutaraldehyde treatment. The beta-galactosidase contained in the stabilized cells was not solubilized when the cell wall was totally digested with exogenous lytic enzymes. Thus, a steric effect mediated by the cell wall was not involved in the insolubilization of the enzyme activity. Actually, the cross-linking reaction gave rise to the formation of an insoluble structure in which the intracellular, and partially the cell wall components, were immobilized. The property of this cluster of being insoluble is independent of the cell wall integrity. This structural feature were confirmed by electron microscopy. The formation of the insoluble structure requires the glutaraldehyde reaction to occur in the intracellular environment. When the cell components were dispersed in the reaction mixture, the cross-linking reaction produces soluble high molecular aggregates containing the beta-galactosidase activity. The beta-galactosidase was inactivated when the stabilized cells were agitated with glass beads, indicating that the whole cell biocatalyst was sensitive to shear stress. Treatment of the stabilized cells with exogenous proteases, such as trypsine, both solubilize and inactivate the beta-galactosidase activity.