Ethyl 5-Methyl-6-oxo-5,6-dihydro-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxylate-d3 is an isotope labelled analog for Ethyl 5-Methyl-6-oxo-5,6-dihydro-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxylate. Ethyl 5-Methyl-6-oxo-5,6-dihydro-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxylate, is used in the biological studies and preparation of imidazobenzodiazepines as probes for diazepaminsensitive receptor pharmacophore.