Pyrolysis of 2-arylimino-3-arylthiazolidin-4-one gives rise to water, aniline, acetanilide, azobenzene, benzonitrile, p-toluonitrile, indole, benzthiazole, 6-methylbenzthiazole, thioglycolic acid, phenylisothiocyanate, p-tolylisothiocyanate, thiocarbanilide, N-phenyl-N-ptolylthiourea, p-aminoacetophenone and N-phenylbenzimidazole. A free radical mechanism has been suggested to account for the formation of the products.