Cystein residues within metallothionein (MT) structure have been shown to be particularly prone to S-nitrosylation. The objective of this study was to examine the possibility that MTs undergo S-glutathionylation under nitrosative/oxidative stress. MT from rabbit liver was treated with different concentrations of GSNO, diamide plus GSH or H 2 O 2 plus GSH. Parallel sets of samples were treated with 10mM DTT for 30min at 37°C to reduce mixed disulphides. Incubations were then processed for Western blot or dot-immunobinding assay. Western blot with anti-MT or anti-GSH were also performed on peripheral blood mononuclear cell extracts. Structural aspects of S-glutathionylation of MTs were also examined. Treatment with GSNO, diamide/GSH or H 2 O 2 /GSH induced a dose-dependent increase in the levels of MT S-glutathionylation. This effect was completely reversed by treatment with the reducing agent DTT, indicating that S-glutathionylation of MT protein was related to formation of protein-mixed disulphides. Structural analysis of rat MT indicated that Cys residues located in the N-terminal domain of the protein are the likely targets for S-glutathionylation, both for their solvent accessibility and electrostatics induced reactivity. S-Glutathionylation of MT, given its reversibility, would provide protection from irreversible oxidation of Cys residues, thus representing a mechanism of high potential biological relevance.