The aim of this study was to assess if, in the neonatal period, there were differences in the blood pressure (BP) level of infants who did and did not develop chronic lung disease. If such differences were demonstrated to exist, we also hoped to determine influencing factors. Forty infants, consecutively admitted to our unit and who remained there throughout the neonatal period were studied. Twenty infants, median gestational age 29 weeks (range 27-32), did not develop CLD (non-CLD group) and 20 infants, median gestational age 26 weeks (range 24-32), developed CLD. Systolic BP was assessed using a non-invasive Doppler technique on day one and subsequently at weekly intervals. After day one and throughout the neonatal period BP levels, corrected for birthweight, were higher in the CLD group compared to the non-CLD group, by a mean of 5 mmHg. There was no significant difference between the numbers of infants in each group receiving theophylline or pancuronium. Significantly more infants in the CLD group had an umbilical catheter inserted and their catheters remained in situ significantly longer, a median of 8 days compared to a median of one day in the non-CLD group. We conclude that even in the neonatal period infants who develop CLD may have a modest elevation of BP, this is associated with prolonged umbilical arterial catheterisation. Our results, however, suggest that significant hypertension in infants who develop CLD, occurs after the neonatal period.