The thesis evaluates the role of procalcitonin in the differential diagnosis of infectious and non-infectious etiology of the systemic injlammatory response by the body and compares it with the value of traditional markers of injlammation. Part two of the thesis evaluates the determination of serum procalcitonin levels in the early post-operative period in patients after liver transplantation. A total of 407 procalcitonin samples form 124 patients divided roto four diagnostic groups: 0 - localized infection (88 studies), 1- SIRS (100 studies), 2 - sepsis (1 h5 studies), 3 - severe sepsis and septic shock (54 studies) were examined. The groups were further subdivided roto subgroups of patients with and without immunosuppressive therapy. The values obtained were compared with those of CRP, IL-h and WBC in the samo groups of patients. In septic shock patients, changes in the serum levels of PCT and CRP were monitored on three consecutive days in survivors as well as in those who diod. Compared with the other markers of injlammation (CRP, IL-h, and WBC), procalcitonin is oné showing the highest sensitivity and speciffcity in the differential diagnosis of infectious and non-infectious etiology of SIRS. The „cut-off" value for sepsis prediction is 2 ng/ml with a sensitivity of 9h% and a speciffcity of 8h%. The highest diagnostic benefit of PCT has been shown in patients with immunosuppressive therapy in whom, among all the markers tested, it has been identified as the only predictor of the infectious etiology of SIRS, with the „cut-off" value of 2 ng/ml associated with a 100% sensitivity anda speciffcity 93.1 %. In septic shock, the decrease in the serum levels of PCT was significant on days 1 to 3. A daily decrease by a minimum of S ng/m/l was seen in all of them. Prokalcitonin is a reliable measurable marker of the clinical course in patients with infectious complications. In liver transplant recipients, serum PCT levels were examined still before infuction of anesthesia, at hours 4 and 8 following graft reperfusion, and daily until post-operative day 4. The patients were divided roto a group receiving polyclonal antibodyATG Fresenius (21 patients) and oné without it (7 patients). Polyclonal antibody administration to patients with liver transplantation is associated with a vety marked increase in serum PCT levels, with peak values on post-operative day 1, this, however, without a clinical correlate in the form of a severe inflammatory response by the body. In cases where polyclonal antibody was not administred, there was only a mild incerase in PCT levels. Numerous issues regardin the site of PCT production, regulation of its synthesis, and its physiological value as well as its value in pathological conditions still remain to be answered.

        Key words: procalcitonin - infection - sepsis - liver transplant patients - pan-T-cell antibodies