A new class of radiation-protective compounds has been found in the bis (methy1thio) and methylthio amino derivatives of 1-methylquinolinium-and 1-methylpyridinium-2-dithioacetic acids. The compounds gave good protection to mice VI. 1000-rad y-radiation in ip doses of 10 mg/kg or less, much lower than those required for the aminoalkyl thiols (-150-600 mg/kg). The dithioacetic acid zwitterions were prepared from the base-catalyzed reaction of ...