INTRODUCTION. Diffuse peritonitis remains a topical problem of modern medicine and is still associated with high mortality. The OBJECTIVE of this work was to develop an objective and easy-to-perform method for determining the indications for programmed relaparotomy in patients with diffuse peritonitis on the basis of determining the aggressiveness of its course.MATERIAL AND METHODS. The work was based on the results of treatment of 100 patients with diffuse peritonitis. Depending on the pH of the exudate of the peritoneal cavity, the patients were divided into 2 groups. The first group consisted of patients with pH value of peritoneal exudate more than 6.2 (75 patients), and the second group consisted of patients with pH value of peritoneal exudate 6.2 and less (25 patients).RESULTS. As a result of the treatment in group I, the mortality rate was 12.0 %. In group II, the mortality rate was 56.0 %. The difference was statistically significant (p<0.001). In group I, 4 patients underwent relaparotomy (5.3 %), and in group II, 17 patients underwent relaparotomy (68.0 %). The difference was statistically significant (p<0.001).CONCLUSION. We concluded that at pH value of exudate 6.2 or less and the absence of obvious clinical improvement, the patient had been showed to performance the programmed remedial relaparotomy no later than 48 hours from the first operation.The authors declare no conflict of interest.The authors confirm that they respect the rights of the people participated in the study, including obtaining informed consent when it is necessary, and the rules of treatment of animals when they are used in the study. Author Guidelines contains the detailed information.