In order to compare longitudinal data with existing cross sectional extrauterine life data on somatosensory evoked potentials (SEPs), two groups of appropriate for gestational age optimal premature infants were studied. Group A consisted of 8 infants born between 34 and 36 weeks gestational age (GA). In this group, SEPs were recorded within 24 hours after delivery and then every 48-72 hours until discharge. Group B consisted of 7 infants born between 29 and 33 weeks GA. In these infants, SEPs were recorded at weekly intervals from the second week onwards. In group A, a marked decreased in the N1 latency was seen during the first week of life. Six infants had initial values above the normal range. During the second week of life this decrease paralleled the cross sectional data. In group B all the infants had a N1 latency within the normal range and the longitudinal data paralleled the cross sectional data. These findings must be taken into consideration when SEPs are used to assess the neurological integrity of the newborn during the first week of life.