Nitric oxide (NO) has recently been found to be the endothelium-derive
d factor that produces profound relaxation of the vascular smooth musc
le. This discovery has led to the experimental use of inhaled NO as a
selective pulmonary vasodilator without concomitant systemic vasodilat
ion. Currently, clinical trials of inhaled NO in persistent pulmonary
hypertension of the newborn (PPHN) are in progress. Inhaled NO has als
o been used in the adult respiratory distress syndrome (ARDS). The the
rapeutic role, if any, of inhaled NO in other diseases featuring pulmo
nary hypertension remains unknown. Further research is needed to deter
mine potential toxic effects of NO, development of delivery systems, a
nd monitoring techniques applicable to routine clinical care.