The (S) and (R)-[I-123]iodinated analogues of the benzodiazepine receptor partial agonist bretazenil have been synthesised for study of the central benzodiazepine receptor using SPECT. (S)- and (R)-[I-123]iodobretazenil were prepared from the appropriate tin precursors by electrophilic iododestannylation with Na[I-123] in the presence of Chloramine-T. The products were purified by semi-preparative reverse-phase HPLC with radiochemical yields of 80% in a total synthesis time of 50 minutes. The specific activity Cas determined to be greater than 2500 Ci/mmol. The radiochemical and chemical purity assessed by radio-TLC and HPLC were found to be 98%. The enantiomeric purity of the (S) and (R) isomers were greater than 97% as assessed by analytical chiral HPLC analysis.