Laparoscopic surgery necessitates the description and definition of the various biochemical and physiological effects of pneumoperitoneum in the body. We report the preliminary results of an experimental study investigating the changes in serum nitric oxide levels in rats undergoing laparoscopic (LBTV) versus open (OBTV) bilateral truncal vagotomy. Thirty-six Wistar-albino rats were divided into 3 groups including the control (n:6), laparoscopy (n:15) and open (n:15) group. Controls underwent laparotomy with a 5 cm midline incision and were sacrificed after blood was drawn from inferior vena cava for baseline values. LBTV was effected with 3 mini-trocars. Pneumoperitoneum was maintained at 6-7 mm Hg. OBTV was performed with a 5 cm midline incision. Both of the procedures lasted 30-35 minutes. In each group, laparotomy was performed either 6 hours (n:5), 12 hours (n:5), or 24 hours (n:5) after the first operation and blood for analysis was obtained by puncturing inferior vena cava. Serum NO2-/NO3- (stabile end-products of NO) levels were determined spectrophotometrically by the Griess reaction, As a results, serum nitrate and nitrite levels were found to be depressed on both the LBTV and OBTV groups at 12 hours compared to controls, however, this difference was statistically significant only in the OBTV group (6.79 +/- 0.81 mu M versus 16.46 +/- 7.43 mu M, respectively: p < 0.05, Mann-Whitney U). In both groups, serum nitrate and nitrite levels were similar to controls at 6 and 24 hours (p > 0.05, Mann-Whitney U). These preliminary results suggest that bilateral truncal vagotomy performed by the open technique inhibits NO synthetase in contrast to laparoscopic bilateral truncal vagotomy. This effect may be attributable to inhibitory mediatory released from the larger trauma in the open procedure.