In newborns with postpartum acidosis the subcutaneous interstitiel space pH was monitored continuously with the special electrode of Stamm and Moeller. This was compared with intermittent determinations of the pH in the capillary blood from the heel of the infant. The severity of the metabolic disturbance can be recognized in all test cases with both methods. The correction of the acidosis develops in a concordant manner, in a concordant magnitude and at a largely synchronous rate. The observations show that it is possible to monitor the postpartum adaptation phase by continuous pH monitoring in the interstitial space of the subcutaneous tissue and to observe the efficiency of the treatment of acidosis, administration of oxygen, or a buffer infusion.