Feasibility of hyperbaric oxygen therapy (HBO) as an efficient and safe adjunct to the standardized treatment protocol and its possible immunomodulatory impact were assessed in the prospective and controlled study of 44 patients with diagnosed acute pancreatitis (AP). The course of the disease was accompanied by systemic inflammatory response syndrome (AIRS) in all the patients on admission. The impact of AP and HBO on homeostasis, the number of performed operations, mortality rates, the levels of two cytokines, intraabdominal pressure, and side effects caused by HBO were evaluated. A treatment group consisted of 22 patients receiving HBO therapy for 3 days (twice a day) using a monoplace chamber under pressures of 1.7-1.9 ATA. Patients (n = 22) in the control group were managed in accordance with the standardized treatment protocol. The authors found more stable homeostasis, decreased mortality rate, and the number of operations in the HBO group. This type of additional therapy, possibly contributed to the decrease of intraabdominal pressure within the first six days after admission. The findings suggest HBO can affect an inflammatory response, by decreasing the levels pro-inflammatory cytokines and increasing those of anti-inflammatory ones.