4-Chloro-benzoic Acid 1-(4-Methoxyphenyl)hydrazide Hydrochloride-d4 is the isotope labelled analog of 4-Chloro-benzoic Acid 1-(4-Methoxyphenyl)hydrazide Hydrochloride (C364430); a useful synthetic intermediate for the preparation of Indomethacin (I641000); a potent, time-dependent, nonselective inhibitor of the cyclooxygenase enzymes COX-1 and COX-2.