Six consecutive cases of persistent pulmonary hypertension of the newborn (PPHN) were treated with adenosine following failure of conventional therapy, excluding inhaled nitric oxide. A rise in arterial P_O2 >20 mm Hg occurred in 5 of 6 cases within 30 min of commencing adenosine infusion. Individual maximal increases in PaO₂ ranged from 31 to 131 mm Hg. Three neonates survived and 3 died. Amongst deaths, intensive support was withdrawn in a preterm neonate due to severe arthrogryposis/pulmonary hypoplasia. Of the remaining 2, the improvement in oxygenation persisted until death occurred from causes unrelated to adenosine. Side effects related to adenosine (bradycardia, hypotension, prolonged bleeding time) did not occur. Due to its ease of availability, administration and extremely short half-life, adenosine may be an important therapeutic option in PPHN.