The title compounds - arenediazothioethanoic acids and 2-arenediazothiopropanoic acids - have been synthesized by the coupling of arenediazonium phosphates with 2-mercaptoacetic or 2-mercaptopropanoic acid in aqueous media at pH approximate to 4. Included are hitherto unreported benzenediazothioethanoic acid and 2-benzenediazothiopropanoic acid prepared in pure form, as well as a number of mostly para ring-substituted examples. Mass spectral fragmentation patterns of selected title compounds are discussed, along with a brief preliminary account of their Z/E-isomerization and thermal stabilities. [GRAPHICS] .