Blood pressure was retrospectively studied in all 22 extremely low birth weight infants (ELBW) (birth weight median 720 g, range 450-1020 g) who were admitted between July 1989 and October 1991 and received dexamethasone on days 2-25 (median 10) because of bronchopulmonary dysplasia or since lung function had not improved after installation of bovine surfactant. The average blood pressure during the 4 h before dexamethasone increased significantly (median individual increase 8 mmHg, P = 0.0005) until 8-12h thereafter. In addition to the lung disease, ten infants showed severe arterial hypotension with prolonged capillary refilling time ( > 3s) and oliguria and needed continuous infusion of epinephrine to increase blood pressure and urinary flow after treatment with colloids, dopamine and dobutamine had proved ineffective. Epinephrine infusion could be stopped in eight infants 8 h after dexamethasone administration. In ELBW infants blood pressure rose 8-12 h after a single dose of 0.25 mg/kg dexamethasone. In ELBW infants suffering from arterial hypotension who do not respond to infusion of colloids and catecholamines, dexamethasone may represent a new therapeutic tool.