Some indices of humoral and cellular immunity were studied in 98 patients with diabetes mellitus (DM), complicated with pyoseptic infection (phlegmon, abscess, gangrene of different sites, hematogenic osteomyelitis, furunculosis, sepsis). A course of hyperbaric oxygenation (HBO) was conducted. Multimodality antidiabetic therapy in combination with HBO resulted in the improved general status of almost all DM patients, stimulation of reparative processes and wound defect closure were faster; DM compensation was achieved and ketoacidosis stopped. Normalization of laboratory and clinical indices was accompanied by immunological tests. The use of HBO in multimodality therapy of patients with DM complicated with pyoseptic infection brings about a good therapeutic effect.