Preterm birth and chronic lung disease may increase the risk of hypertension and cardiovascular disease in infancy and adolescence. Here we looked for evidence of early circulatory dysfunction associated with these perinatal complications. We compared infants born at term (n ϭ 12) with those born preterm with an uncomplicated neonatal course (n ϭ 12) or diagnosed with bronchopulmonary dysplasia (BPD) (n ϭ 10). We measured blood pressure (BP) (Finometer), and heart rate (HR) responses to 4 min of breathing 4% CO 2 during quiet sleep. Hypercapnia accelerated HR and increased BP of term infants. Preterm infants either (i) had an exaggerated pressor but little or no HR response to CO 2 (healthy or mild-moderate BPD) or (ii) had a diminished pressor response and accompanying decrease in HR (severe BPD). Short-term reflex cardiovascular control was consequently altered by premature birth, with potentially more serious aberrations associated with severe BPD. Most anomalies had not resolved by the time infants born preterm reached term age; some may be early signs of emerging long-term cardiovascular dysfunction. W ith the impressive increase in survival of very preterm and low birth weight infants come new challenges. Evidence already indicates that this "new generation" of children and adolescents may have accelerated disease onset later in life (1). One factor contributing to their higher risk of cardiovascular disease may be abnormal vascular and circulatory development (2-4). Cardiovascular activity is normally carefully regulated, but if some or all of the central and peripheral regulatory mechanisms involved fail to develop normally, perfusion, growth, and function may be compromised. In exceptional circumstances during infancy, persistent serious dysfunction could result in a sudden catastrophic decrease in BP and HR or prevent autoresuscitative recovery, culminating in sudden infant death syndrome (SIDS) (5,6). In other cases, dysfunction may be relatively benign, although there may still be side effects with adverse consequences of their own.We know relatively little about how BP and HR control develops, and the potentially adverse effects of fetal and perinatal stress. A better understanding of these issues could lead to new therapies or strategies to prevent neonatal complications and improve long-term outcome. In the study described here, we looked for evidence that development of neonatal circulatory control is altered by common perinatal complications (7). We studied three different groups of newborn infants: those born normally at term, those born preterm but otherwise healthy, and infants born very preterm suffering from chronic lung disease (BPD). Infants with BPD are at particularly high risk of long-term cardiovascular complications and SIDS (8 -10). We compared BP and HR responses of these infants to a routine physiologic stress (breathing a low concentration of CO 2 for several minutes) commonly used to unmask autonomic anomalies (11). Normally, acute exposure to CO 2 increases BP and HR ...