Previous studies have suggested that ciamexone, a 2-cyan-aziridine derivative, is a selective immunomodulatory agent with potential therapeutic application in a variety of autoimmune diseases. In the present study, the effects of ciamexone on autoimmune lymphocytic thyroiditis and diabetes mellitus were studied in the BB rat. The data suggest that, in this animal model, ciamexone does not affect the frequency of autoimmune diabetes or lymphocytic thyroiditis nor does it affect the serum TSH or T4 concentrations.