The conformation of 1,4-benzodiazepines that is recognized by the binding site on the benzodiazepine receptor complex in the mammalian brain, may be one in which the planes formed by the fused benzene ring and the methylene group (and the 2 adjoining atoms) of the diazepine ring are in the R configuration. The derivation of this conformation was based on comparisons of computer-generated 3-dimensional structures obtained from single-crystal X-ray data for diazepam (R)- and (S)-1,3-dimethyl-5-(2-fluorophenyl)-7-nitro-1,3-dihydro-2H-1,4-benzodiazepin-2-one, and the structurally rigid ethyl (S)-7-chloro-11,12,13,13a-tetrahydro-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-d][1,4]benzodiazepine-1-carboxylate. The affinity of ligands for the benzodiazepine binding was determined [in mammalian brain] using the [3H]-diazepam binding assay.