Three groups of neonates were observed during their first 5 days of postnatal life. Healthy term babies (N = 22) did not differ in their heart rate variability (HRV) nor heart rate (HR) from the healthy preterm babies (N = 21) during the first 3 days. On day 5 beat-to-beat variability of term babies was greater. In healthy term and preterm infants HRV increased between days 1 and 3. HRV of the babies with respiratory distress syndrome (RDS) (N = 1) remained low throughout the study period. HR of the babies with RDS was significantly higher compared to the other groups on the days 1 and 3. Transcutaneous PO2 was high in healthy preterm infants compared to the other groups. The correlation between PaCO2 and PtcO2 in RDS was insufficient to make clinical judgement. PtcCO2 of all neonates tended to rise on the day 5 but the rise was most prominent in the infants with RDS. The correlation of PaCO2 and PtcCO2 was good. In RDS high HR, low HRV and elevated PtcCO2 were the typical findings and present throughout the study period.