Three parameters participating in the specific control of proteolytic processes in intact yeast cells are discussed: (1) different substrate specificity of the yeast proteinases A and B, and carboxypeptidase Y when tested with yeast enzymes as substrate, (2) three types of macro- molecular inhibitors from yeast specifically inhibiting the three pro- teinases, (3) subcellular localization of the proteinases in the vacu- oles and of the inhibitors in the cytosol. Mechanisms of a selective proteolysis of single enzymes or a group of enzymes dependent on chan- ges in the physiological conditions are discussed. References Betz, H., Hinze, H., Holzer, H.: Isolation and properties of two inhibitors of proteinase B from yeast. J. Bioi. Chem. 249, 4515-4521 (1974) Cabib, E., Farkas, V.: The control of morphogenesis: An enzymatic mechanism for the initiation of septum formation in yeast. Proc. Nat. Acad. Sci. U.S. 68, 2052-2056 (1971) Cabib, E., Keller, F.A.: Chitin and yeast budding. J. Bioi. Chem. 246, 167-173 (1971) Cabib, E., Ulane, R.: Chitin synthetase activating factor from yeast, a protease. Biochem. Biophys. Res. Commun. 50, 186-191 (1973) Hasilik, A.: Inactivation of Chitin Synthase in Saccharomyces cerevisiae. Arch. Microbiol. 101, 295-301 (1974) Hasilik, A., Holzer: PartiCipation of the tryptophan synthase inactivating system from yeast in the activation of chitin synthase. Biochem. Biophys. Res.