Background/Aims: Recognized laboratory criteria for acute intra-abdominal infection, in particular, general blood test, C-reactive protein, are nonspecific and insufficiently informative. We previously reported on the results of venous plasma optical density (ODVBP) measurements in emergency abdominal surgery. But the examined patients differed in the type of disease, sex, etc. Therefore, we conducted experimental studies to substantiate the possibility of using such a criterion. Methods: 60

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... te nonlinear mature rats of both sexes, 180 to 200 g weight. To simulate acute intra-abdominal infection, intraabdominal injection of 10 ml of 10% solution of autofaeces per 100 g of weight was performed. Blood from the jugular vein and pieces of peritoneum for histological examination was taken. The studies were performed before simulation, 6, 12, 24 and 48 h after simulation. ODVBP was examined on an Agilent Cary 100/300 Series UV-Vis spectrophotometer. Healthy animals were monitored for control. Results: In healthy animals at a wavelength λ = 310 nm there is a specific maximum ODVBP, reaching 0.22 units. After simulation of acute intra-abdominal infection and the occurrence of serous peritonitis, there was a statistically significant increase in ODVBP at this wavelength. After the onset of purulent peritonitis, ODVBP also increased statistically significantly. Subsequently, after the spread of inflammation to the deep tissues of the abdominal wall, ODVBP was at a high level and statistically significantly exceeded the control values. Conclusions • In healthy white rats at a wavelength λ = 310 nm, a maximum ODVBP was detected, reaching 0.22 units, which does not depend on sex differences. • After simulation of acute intra-abdominal infection and the development of serous inflammation of the peritoneum ODVBP this wavelength increased statistically significantly and reached 0.26 units. • After the development of purulent peritonitis, ODVBP again increased statistically significantly and reached 0.36 units, and then, after the spread of inflammation to the deep layers of the abdominal wall, the indicators were at a high level without significant differences. • The absolute parameters of the indicators differed from those determined in humans, but the ratios due to the presence of inflammatory changes in the abdominal cavity were preserved.