Delay in cord clamping after vaginal delivery increases the blood volume of the newborn. Similar effects have also been observed in cesarean section births. Other effects of delayed cord clamping in cesarean section have not been investigated. In a group of nineteen healthy mothers having elective cesarean sections the cord clamping time was increased from 0 minutes to 1.5 and 3 minutes. Significantly lowered PO2 and pH and elevated plasma lactate levels were observed in infants with 3 minutes' delay when compared with the early clamping group. We conclude that, when healthy mature newborns are considered, early clamping of umbilical cord in cesarean section with general anesthesia is preferable to late clamping.