The introduction of more reliable methods for determining various components in the acid-base status of the blood always arouses renewed interest in the problems that are attacked by means of these analyses. A study of acid-base balance in new-born infants should be of especial interest because birth and the readjustments of the first few days of life subject these infants to influences of a magnitude rarely duplicated in later life. The process of birth with its abrupt increase in the supply of oxygen is as dramatic as the rapid transplantation of a mountaineer to sea level. This sudden environmental change is followed by a few days of partial starvation and relative dehydration, which cause loss of weight and which may result in fever. It is therefore apparent that one may not find adult measurements of the acid-base relation directly applicable to new-born infants. The object of this paper is to