In vivo, noninvasive, transepidermal water loss measurements were taken from 26- to 41-week gestational age infants with a Meeco® electrolytic water analyzer to yield information on the development of the function of the skin barrier. Infants 28 weeks or less have significantly greater transepidermal water loss than older gestational aged infants, thus indicating a less efficient barrier to water. Until it is known whether the decreased barrier function in premature infants also relates to percutaneous penetration, prudence is suggested in exposing such premature infants skin to chemicals.