Plasma arginine vasopressin concentration (pAVP) was determined in 47 patients during the insufflation stage of laparoscopy. Laparoscopy was performed under local anesthesia in 39 patients, and under general anesthesia in 8. Pneumoperitoneum was induced with 3-4 1 nitrous oxide to a maximum intra-abdominal pressure of 10 mm Hg. Induction of pneumoperitoneum resulted in a prompt and significant increase in pAVP in every case. In 34% of cases, pAVP increased two- to fivefold as compared with preinduction levels; in 44.7% of cases, elevations of more than fivefold were seen. Increased arginine vasopressin secretion was not related to underlying liver disease, degree of anxiety, changes in blood pressure, heart rate, pCO2, pO2, serum bicarbonate or plasma osmolality. Elevated pAVP was associated with a significant increase in right atrial pressure. In conclusion, abdominal distension during laparoscopy was accompanied by an increase in pAVP. It seems likely that arginine vasopressin response could be due to a decrease in the left atrial transmural pressure gradient.