The rearrangement product of the toluene-p-sulphonylester of N-hydroxy-N′N″-diphenylguanidine reacts with pyridine or γ-picoline to give anhydro-1-phenyl-3-phenylimino-s-triazolo[4,3-a]pyridinium hydroxide or its 7-methyl derivative; the structure of the 7-methyl derivative has been unambiguously assigned by X-ray analysis and chemical considerations.