By means of 522 singles in breech presentation the pH of umbilical artery (pH u. a.) and Apgar score in comparison to the mode of delivery, duration of pregnancy and weight of neonates have been analysed. The frequency of deliveries by cesarean section in breech presentation was 28.3%, the rate of preterms in these cases amounts to 14.6% and the perinatal mortality to 42.1%. The average value of pH u.a. after vaginal delivery (7.25) was significantly different to the value after cesarean section (7.28). 25% of the pH-values were below 7.20, 10% below 7.10. Mixed acidoses dominated, metabolic ones after vaginal and abdominal deliveries equalled each other. Vaginal deliveries were frequently followed by respiratory acidoses. In 81% of one-minute-Apgar and in 93% of five-minute-Apgar, the score was above 7. According to our experiences the only determination of the pH u.a. after breech deliveries is not sufficient, because of being at risk for the fetus it demands the measurement of the complete acid-base-status. A critical comparison of these data with the clinical status of the newborn is necessary.