Thermal or photolytic reactions of bioactive S-nitrosothiols and related thiols in the presence of radical generators in deaerated DMSO or aqueous solutions under argon or saturated with nitric oxide (NO) produced nitroxides and an oxyaminyl radical, which were well characterized by EPR spectra. Nitroxides containing a thiyl substituent were obtained. Possible mechanisms are proposed. Bioactive S-nitrosothiols such as S-nitrosoglutathione, S-nitroso-N-acetylpenicillamine and related thiols such as glutathione and N-acetylpenicillamine were used for the investigation. Radical generators utilized as transient radical sources were 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylpropionamidine) dihydrochloride, tert-butyl peroxide and benzoyl peroxide.