Hypothermia is a common postsurgical problem, yet information documenting the impact of laparoscopy on perioperative heat balance is scarce. This paper quantifies the changes in core temperature over a 3-h period of high-flow CO2 insufflation in a randomized, controlled trial of six pigs. Each animal was anesthetized and studied on three occasions under standardized conditions, acting as its own control via insufflation with no gas compared with insufflation by cold gas and warmed gas. Insufflation of CO2 gas at high-flow rates over a prolonged period of time results in a significant fall in core temperature. The provision of warmed rather than cold insufflated gas confers no protection against changes in core temperature during laparoscopic surgery due to the small amount of heat required to warm the gas to body temperature. A much greater effect is the latent heat required to saturate the insufflated gas. Most of the hypothermic effect is due to this, and could be minimized by humidifying the flow.