Endothelins (ETs) are highly vasoconstrictive 21-amino acid peptides possessing also cell-proliferative properties. They have been implicated in a variety of perinatal pathologic conditions, and their plasma concentrations have been found elevated in humans at birth. The purpose of this study was to determine ET 1-21 plasma concentrations in healthy and ill preterm infants and to investigate possible concentration changes with time from birth in cases of normal and abnormal adaptation to extrauterine life. The study comprised 36 preterm infants. Twenty-eight, comprising group A, were healthy (22/28) or minimally affected (6/28) and 8, comprising group B, were moderately (2/8) or severely ill (6/8) requiring continuous positive airway pressure or intermittent positive pressure ventilation as well as surfactant administration. All infants in group B had intraventricular hemorrhage grade > or = II. Venous blood from all neonates was drawn on days 1 and 4 and ET 1-21 plasma concentrations were determined by radioimmunoassay (Amersham kit RPA 5559). ET 1-21 plasma concentrations were on day 1: 16.25 +/- 8.14 and 21.81 +/- 5.87 and on day 4: 12.89 +/- 4.56 and 16.16 +/- 5.43 pmol/l, for groups A and B, respectively. The statistical analysis showed a significant reduction in plasma ET concentrations on day 4 in both groups (p = 0.009 and p = 0.025, respectively). Nevertheless, ET 1-21 plasma concentrations were on day 4 significantly higher in ill preterm infants presenting symptoms from tissues involved in the elimination of ETs from the circulation as well as in their production.