Recently developed techniques of video-endoscopic surgery may offer new hope for the future of fetal surgery. To allow this approach, the amniotic cavity has to be temporarily enlarged, either by carbon dioxide (CO2) insufflation or by amnioinfusion. In 6 anesthetized ewes, CO2 insufflation of the amniotic cavity produced severe fetal hypercapnia (from 57.6 ± 1.6 to 87.0 ± 7.0 torr) and acidosis (from 7.22 ± 0.03 to 7.11 ± 0.08) despite normal maternal CO2 pressure and pH. CO2 pneumoamnios does not therefore appear to be an ideal working medium. Fetal endoscopic surgery through amnioinfusion of physiologic fluid may be a safer alternative.