Brain natriuretic peptide (BNP) relaxes guinea pig tracheal smooth muscle in vitro and is effective in preventing ovalbumin-induced bronchoconstriction and microvascular leakage in guinea pigs in vivo. Nonetheless, published studies on BNP in human airways in vitro are still lacking in the literature. The aim of this study was to investigate the effect of BNP in isolated human bronchi. The relaxant effect of BNP (1 nM to 10 microM) was assessed in nonsensitized and in passively sensitized human bronchial airways pre-contracted with submaximal concentration (EC(70)) of carbachol or histamine. At the end of the experiment, papaverine (500 microM) was then added. BNP induced a weak relaxant activity on carbachol-contracted bronchi in nonsensitized (relaxation: 4.23+/-0.51%) and passively sensitized bronchi (relaxation: 11.31+/-2.22%). On the other hand, BNP induced a relaxant activity on His-contracted bronchi in nonsensitized (relaxation: 42.52+/-9.03%) and in passively sensitized (relaxation: 60.57+/-9.58%). All these findings are a clear documentation of the modest relaxant role of BNP in asthma and, likely, COPD.