The preparations of guvacine hydrochloride, in which a proton in position 2 (11) and protons in positions 2 and 5 (10) are selectively exchanged by deuterium, and of [2,6‐²H]isoguvacine hydrobromide (14a) are described. The deuterium labelled guvacine salts 10 and 11 were synthesized by triethylamine catalyzed exchange of hydrogen for deuterium in methyl N‐nitroso‐1,2,5,6‐tetrahydropyridine‐3‐carboxylate (3) followed by denitrosation and hydrolysis. Treatment of N‐nitroso‐1,4,5,6‐tetrahydropyridine‐3‐carboxylic acid with methanolic thionyl chloride gave 3,4,5,6‐tetrahydropyridin‐3‐on ketoxime. Compound 14a was prepared by sodium borodeuteride reduction of 4‐ethoxycarbonyl‐1‐methylpyridinium iodide (12) followed by N‐demethylation and hydrolysis of the intermediate.