Nitrates (NO 3 ) are metabolites of NO which have been used as markers of endothelial activity. NO is measured in expired air in asthmatics patients to study the inflammatory reaction of airway's endothelium. A few studies apply this technique in cardiovascular patients as a measure of changes in endothelial activity. However, to our knowledge there is no study that correlates these two techniques. So, the aim of this work is to evaluate, in the same group of patients, the levels of NO 3 in blood and the levels of NO in expired air. We have studied 10 controls (GI) free of cardiorespiratory disease and 9 asthmatics. We determine the NO in expired air with a Sievers 280 analyser and at the same time the NO 3 in blood using the same equipment. We have obtained the following results: NO mean: GI-21.7 ppb; GII-33.1 ppb; p<0.05; NO 3 mean: GI- 29.2 μmol; GII - 42.5 μmol; p<0.07. We have correlated all the values of NO and NO 3 and found a positive and significative correlation r=0.87 (p<0.01).In conclusion:1) the strong correlation between the NO in expired air and NO 3 in blood allows the use of the former technique as an indirect evaluation of endothelial activity; 2) asthmatic patients present also higher levels of NO 3 that, to our knowledge, have not been referred in the literature.