Introduction

Abstract

Summary The insensible water loss through the lungs and the body surface of newborn infants has been measured for the first time directly. A total of 343 single measurements with 48 new‐ born infants of both sexes, younger than 28 hours, was performed. The significances of the results were statistically evaluated. Of our findings the following are the most important: 1. The insensible water loss under basal conditions is between 390460 mg/kg body weight and hour (mean values of classes O and A′), or between 6.36‐7.47 g/m2 body surface and hour (environment: temp.: 30.5–33.8°C; rel. humidity:37.2–55.5%). 2. During the first 24 hours of life the water loss is independent of the age. 3. There has only been a slight indication that there is a difference between sexes in this age group; the values for females are a little higher, but this is on the border of being sig‐nificant. 4. The mode of sleep is of great influence on the insensible water loss. On the average, long‐ sleeping infants lose much less water than short‐sleeping infants. 5. The insensible water loss greatly in‐creases with increasing activity of the infant. So far it has only been suspected that there is such an increase, however, the increase was never quantitatively determined. This increase is, according to our measurements, at least given by a factor of 1.7; it is very likely that with infants who cry intensively this increase is considerably larger.