High lethality in peritonitis and the data about the role of nitric monoxide in its pathogen‑ esis, determines the feasibility of the research to study effects of the NO‑synthase substrate – L‑arginine. The aim of the research was to study the acute experimental peritonitis course in rats with administration of the NO‑synthase substrate – L‑arginine. The experiments were carried out on male rats, divided into 3 series and intraperitoneally injected with: series 1 (control) – 0,9% sodium chloride, series 2 (experi‑ mental peritonitis) – 15% fecal suspension, 0,6 ml/100 g, series 3 (EP+L‑Arg) – 15% fecal suspension, 0,6 ml/100 g, followed by intramuscular administration of L‑arginine, 300 mg/kg. Administration of the NO‑synthase substrate – L‑arginine to rats with experimental peritonitis had a corrective effect in the form of a decrease in the severity of intoxication syndrome, the reaction of leukocytes of blood and peritoneal fluid, changes in nitrites/nitrates level, a decrease in the activity of oxidative stress, endothelial dysfunction and the degree of damage to peritoneum.