Immune sera specific to bacterial cells at various development stages of periodic culture have been obtained with the purpose to study serological properties of lysin producer. Using the method of immunoenzyme analysis ELISA it is shown that there is certain dependence between the producer properties and the culture age. Different strains-producers used in production to-day are serologically close between each other. When using 49 strains-contaminants of lysin production (representatives of 10 genera) the absence of serological affinity between the producer and foreign microflora has been demonstrated. Preliminary data prove the prevalence of cells producers of thermostable antigens on the cell surface.