The character of the microflora, its antibiotic sensitivity, the titers of lysozyme and beta-lysines, the phagocytic activity of the leucocytes and the number of the T-cells were studied in 52 patients with chronic osteomyelitis before and 5-8 days after the treatment with antibiotics or their combinations with proteolytic enzymes. Pathogenic staphylococci alone or in association were isolated in 92.3 per cent of the patients. The microbiol flora had multiple drug resistance in 80.6 per cent of the cases. It was shown that phagocytosis in the patients was significantly lowered, the lysozyme titer was decreased and the titer of beta-lysines was not markedly changed. As a result of the treatment the lysozyme titer and phagocytosis increased and the number of the T-cells lowered especially in the patients subjected to combined therapy with antibiotics and proteolytic enzymes. The antimicrobial therapy with the use of the enzymes provided a decrease in the bacterial contamination and antibiotic resistance. The results of the study enable prediction of the disease course and therapy efficacy with regard to the immunogenesis, the character of the microflora and its antibiotic resistance.