Abstract In vivo, cysteine in proteins or glutathione is the major amino acid involved in sulfhydryl oxidation-reduction reactions. An in vitro model of cysteine oxidation accelerated by selenium compounds was used to study the interaction of selenocystine and sodium selenite with metal ions. The interaction of metal ions with selenium compounds inhibited cysteine oxidation. The ionic forms of three toxic soft-acid metals, mercury, silver, and gold, were the most effective inhibitors. The antiarthritic gold drugs, aurothiomalate and aurothioglucose, were of particular interest as they inhibit the activity of selenium-glutathione peroxidase. The effect of gold ligands on gold(I) inhibition of selenocystine-accelerated cysteine oxidation was tested. Sodium cyanide partially reversed inhibition and potassium iodide had no effect. Inhibition of selenium-accelerated oxidation-reduction reactions by soft-acid metal ions may be of biological relevance during toxicities or during antiarthritic gold therapy.