Inhaled nitric oxide (NO) is a highly selective pulmonary vasodilator. It was recently reported that inhaled NO causes peripheral vasodilatation after treatment with a NO synthase (NOS) inhibitor. These findings suggested the possibility that inhibition of endogenous NOS uncovered the systemic vasodilating effect of NO or NO adducts absorbed via the lungs during NO inhalation. To learn whether inhaled NO reduces systemic vascular resistance in the absence of endothelial NOS, we studied the systemic vascular effects of NO breathing in wild-type mice treated without and with the NOS inhibitor N(omega)-nitro-l-arginine methyl ester and in NOS3-deficient (NOS3(-/-)) mice. During general anesthesia, the cardiac output, left ventricular function, and systemic vascular resistance were not altered by NO breathing at 80 parts/million in both genotypes. Breathing NO in air did not alter blood pressure and heart rate, as measured by tail-cuff and telemetric methods, in either awake wild-type mice (whether or not they were treated with N(omega)-nitro-l-arginine methyl ester), or in awake NOS3(-/-) mice. Our findings suggest that absorption of NO or adducts during NO breathing is insufficient to cause systemic vasodilation in mice, even when endogenous endothelial NO production is congenitally absent.