Bucillamine [SA96:N-(2-mercapto-2-methylpropanoyl)-L-cysteine] is a synthetic SH compound and an antirheumatic agent developed from tiopronin. It is mainly used in Japan and Korea. Activity is mediated by the two thiol groups that the molecule contains. Research done in the USA showed positive transplant preservation properties. Bucillamine has the potential to attenuate or prevent damage during myocardial infarction, cardiac surgery and organ transplantation. Bucillamine is a more potent thiol donor than other cysteine derivatives: approximately 16-fold more potent than N-acetylcysteine (Mucomyst(R)) in vivo. In addition bucillamine appears to have additional anti-inflammatory effects unrelated to its antioxidant effect. Oral bucillamine is used clinically in Asia for treatment of rheumatoid arthritis. There is a strong preclinical evidence that parenteral infusion of this agent is efficacious in acute settings characterized by inflammation and oxidative stress. In Phase I human trials healthy volunteers received bucillamine at doses up to 25 mg/kg/h i.v. for 3 h and elicited no serious toxicity. On the basis of pharmacokinetic analyses of blood levels during these studies, it was concluded that bucillamine infused at i.v. doses > or =10 mg/kg/h for 3 h to humans could be expected to be therapeutically effective in myocardial infarction, organ transplantation and other acute inflammatory syndromes. Bucillamine exhibits potent antioxidant activity similar to those of trolox and ascorbic acid. It reduces the stable free radical diphenyl-2-picrylhydrazyl (DPPH). Bucillamine is a potent antioxidant which exerts its beneficial therapeutic activities in RA patients by metal chelation rather than by scavenging free radical species.