OBJECTIVE Increased intra-abdominal pressure during laparoscopic cholecystectomy changes pressure values in the thoracic cavity, in blood vessels, and in biochemical blood values. METHODS In this prospective study, we investigate whether CO2 pneumoperitoneum causes blood absorption and whether there is an increased risk of thromboembolism because of its mechanical influence on reographic and biochemical blood attributes. We analyzed pH, BE and arterial blood pCO2 pre-operatively, three times during surgery and post-operatively; and blood coagulation values pre-, during and 30 minutes after the operation. Blood samples were taken from 75 patients, divided into two groups. The first group consisted of 50 patients on whom laparoscopic cholecystectomies were performed, while the second (control) group consisted of 25 patients who were operated on by open laparotomy. All patients had a pre-operative physical status of ASA I and ASA II. RESULTS There was no statistically significant difference in pCO2 in any measurement, but in the group of patients treated with a laparoscopy there were statistically significant increases in pCO2 in three measurements during the operation. CONCLUSIONS The data show that during the laparoscopy the pneumoperitoneum had no physical or biochemical influence on coagulation values and so reduced the risk of thromboembolism.