The effects of different pressure values of pneumoperitoneum on the activity of the autonomic nervous system (ANS) have not been investigated in detail. In this prospective study, 20 patients qualified for laparoscopic cholecystectomy were randomised to either low-pressure (LP = 7 mmHg) or standard-pressure (SP = 12 mmHg) pneumoperitoneum groups, 10 patients each. The anesthesia was induced with fentanyl and thiopental and maintained with isoflurane. Ventilation was mechanically controlled (18 breaths per minute, end-tidal CO2 30-35 mmHg, instant capnometer monitoring). Intraabdominal pressure was maintained automatically by a CO2 insufflator. Patient were kept in a horizontal position. The ANS was evaluated by heart rate variability (HRV) analysis (POSTER ECG 2002 System) measured intraoperatively in three recordings of 5 minutes each: in awake patient, after induction of general anesthesia, and after creation of pneumoperitoneum. Power spectral analysis of HRV was applied, the low-frequency (LF = 0.05-0.15 Hz) and high frequency (HF = 0.15-0.45 Hz) spectral density of the HRV were analysed using the Fast Fourier Transform algorithm. The appropriate statistical analysis of data was performed. LF density decreased at the anesthetized stage and increased at the insufflated stage in both groups (p < 0.01). LP resulted in lower sympathetic activation than SP pneumoperitoneum (LF: 68.12 +/- 6.56 nu vs. 78.26 +/- 5.43 nu, p < 0.01; HF: 24 +/- 2.48 nu vs. 15.56 +/- 2.54 nu, p < 0.05). IN CONCLUSION: pneumoperitoneum leads to sympathetic activation of the ANS. LP in comparison to SP pneumoperitoneum with carbon dioxide results in significantly decreased sympathetic activation during laparoscopy.