The composition of exudates can have its own diagnostic value. Aim — the purpose of the study was to evaluate the content of PCT in the blood serum and peritoneal exudate in different course of the early postoperative period in patients with acute surgical pathology of the abdominal cavity organs. Material and methods. The concentration of procalcitonin (PCT) in blood serum and abdominal exudate was studied in 111 patients with different postoperative course. The main group (n=51) consisted of patients with pyoinflammatory complications. The comparison group (n=60) included patients with a favorable course of the postoperative period. The concentration of PCT was determined by ELISA using the test system “Procalcitonin — EIA — BEST” (Vector-Best, Russia). Results. The content of PCT in the serum of the patients of the main group was 3.75 ng/ml (interquartile range: 1.90—6.32) and exceeded the values of the comparison group, 0.165 and 0.057—0.59 ng/ml, respectively (р<0.001). The concentration of PCT in the exudate was lower than in the blood serum: in the main group 1.42 times and in the comparison group 1.7 times and differed 27 times between the groups (р<0.001). The concentration of PCT in the exudate depended on the serum concentration of PCT, and not on the nature of the exudate. A close positive correlation was found between the content of PCT in blood serum and abdominal exudate (R= 0.91; p<0.001), described by the linear regression equation Y= 0.057+0.6398 X. Conclusions. The obtained data testify to the absence of local production of PCT in the abdominal cavity and its passive penetration from the blood serum into the exudate by the concentration gradient. The most important factor determining the concentration of PCT in the exudate is the content of PCT in the blood serum.