Using a technique based on specific enzyme sorption by chitin (beta-1-4-N-acetylglucosamine), lysozyme with a molecular mass of 15,000 has been isolated from homogenates of the Ix. persulcatus ticks. Micrococci and staphylococci proved to be most sensitive to lysozyme from the Ix. persulcatus ticks, while E. coli and Salmonella were less sensitive. The minimum inhibitory concentration of lysozyme from Ix. persulcatus was 2-4 times lower than that of egg lysozyme. Lysozyme from the Ix. persulcatus ticks is resistant to heating in acid medium and loses some of its activity in alkaline medium. The loss of the activity in the both media is somewhat lower than that of egg lysozyme in analogous conditions.