A retrospective analysis comparing intraoperative physiological variables during laparoscopic and open pyloromyotomies was undertaken during an 18-month period at our institution. Fifty cases were examined (22 laparocopic and 28 open). Operative time, temperature change, end-tidal CO2, heart rate, and blood pressure were examined and compared. No significant differences were found in operative time, temperature change, heart rate, and blood pressure. As anticipated, in laparoscopic procedures there was a statistically significant increase in end-tidal CO2, although none of the end-tidal CO2 values rose above 6 kPa. It is concluded that laparoscopic pyloromyotomies undertaken in small infants with insufflation pressures of 8-10 mm Hg are without significant adverse physiological effects and are no slower to perform than open procedures.