NO. exerts many effect on the organism, either beneficial or detrimental. Beneficial ones are mainly mediated by NO. itself (through activation of guanylyl cyclase - the cGMP-dependent pathway - or through S-nitrosylation) in a specific microenvironment, generated at low concentrations by endothelial or neuronal NO-synthases in a regulated manner. By contrast, prolonged and high-ouput inducible NOS-derived NO. may exert both oxidative and nitrosative stress, respectively through peroxynitrite-mediated oxidation, nitration and oxidative nitrosylation and through dinitrogen trioxide-mediated nitrosation. Integration of all determinants of the net effect of NO. is complex and is the topic of intensive research for potential adapted, selective and titrated treatment. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. ; SCOPUS: ar.j ; info:eu-repo/semantics/published