Ciamexon is an aziridine derivative with potent immuno-modulating activity developed by German pharmaceutical company Boehringer Mannheim G.m.b.H. for autoimmune diseases treatment. Ciamexon shows promising effects in experimental models of rheumatoid arthritis, diabetes, and obesity without toxic side effects. In animal studies, Ciamexon inhibits the proliferation of autoreactive lymphocytes dose-dependently, without affecting the reaction against foreign antigens. Clinical efficacy evaluation of the Ciamexon in patients with rheumatoid arthritis shows significant, dose-dependent improvement in both the clinical and the biochemical disease activity indexes. The major adverse effects of Ciamexon were hepatotoxicity, diarrhea, and rash.