Abstract: Nitric oxide (NO) has been cited to play an important regulatory role in airwayfunction. Moreover, the NO synthase expression in models of inflammation is documented. Theaim of this study was to investigate, in vitro, the NO modulation of cholinergic responses insham-sensitized and ovalbumin-sensitized guinea pig trachea by using L-arginine (L-ARG), aprecursor of NO synthesis, and L-Ng-nitro-arginine-methyl-ester (L-NAME), an inhibitor of NOsynthase.Our results showed that NO’s ability to modulate cholinergic responses in ovalbuminsensitizedguinea pig trachea is lost. Indeed L-ARG and L-NAME modify acetylcholinesensitivity in sham-sensitized guinea pig but not in ovalbumin-sensitized guinea pig.[...]