The thermotolerant culture of Thermoactinomyces vulgaris PA II-4A was cultivated in the Biotec fermenter to obtain the enzyme preparation with a high proteolytic and lytic activity. Resistance of the cells of Candida utilis and Saccharomyces fragilis (mesophilic and thermotolerant strains) to the lytic action of the enzyme preparation was different. Preliminary treatment of the yeast cells by L-cysteine increased their susceptibility to the lytic action of the preparation. The degree of lysis of the cells depended also on their age: the cells growing during 10-12 hours were lysed easier than the cells cultivated during 24 hours.