It is known that carbon dioxide (CO2) pneumoperitoneum induces fetal acidosis in pregnant ewes. Our aim was to determine changes of the levels of maternal and fetal cytokines interleukin-6, interleukin-8, and tumor necrosis factor α after CO2 pneumoperitoneum in pregnant ewes. Eight ewes with singleton pregnancies of 120 to 140 days gestation were anesthetized and intubated. Insufflation produced modest but significant maternal arterial hypercapnia (an increase of 10.7 mm Hg; P<0.001) and acidosis (a decrease in mean pH of 0.1.04; P=0.0005). Fetal pCO2 was increased by 15.3 mm Hg on average and pH was decreased by 0.11 U on average immediately after desufflation (both P<0.001). No significant difference was observed in the concentration of cytokine in the maternal or fetal blood samples. These results suggest that respiratory acidosis does not lead to the elevation of cytokines in pregnant ewes and fetuses, which may contribute to premature labor. © 2009 Lippincott Williams & Wilkins, Inc.