During laparoscopy the carbon dioxide used to achieve a pneumoperitoneum is absorbed from the peritoneal cavity into the blood. The object of the present study was to clarify certain aspects concerned with anesthetic and ventilatory techniques, mostly in connection with the comparison between the effects of insufflation of either carbon dioxide or nitrous oxide. Anesthesia included ventilation with a volume controlled ventilator in curarised patients. Respiratory volumes were calculated according to the patient's body area. The results show a sharp rise in PaCO2 and a fall in pH after intraperitoneal insufflation with carbon dioxide, while no changes were observed when nitrous oxide was used. The clinical consequences of these findings are discussed.