Taking into account the data on oxidative transformation of hydroxamic acids to form nitric oxide and the similarity of their structure to the hydroxyarginine group being involved in the NO synthesis, we performed the study of biotransformation of salicylhydroxamic acid and N(4)-hydroxyasparagine in the liver tissues. According to the data from ESR spectroscopy, the compounds under study are inefficient NO donors in a biological system and their biological activities are mainly defined by the ability to chelate metal ions.