Several new benzodiazepines were studied with respect to their ability to bind specifically to benzodiazepine receptor sites in rat cerebral cortex membrane fraction. The IC50 values of new benzodiazepines were compared to that of diazepam. A group of triazolo-[1, 4] benzodiazepines displaced ³H-diazepam very effectively. The most potent of this group was brotizolam. Its potency was about ten times higher than that of diazepam. In this study, camazepam, which differs from diazepam in its C-3 substitution, had the lowest affinity to the benzodiazepine receptor site. This potency was about 0.006 that of diazepam. CM 7116 bound with the highest affinity to the benzodiazepine receptor site among the metabolites of CM 6912. The length of the side chain at the C-3 position of this compound is shorter than that of the other metabolites of CM 6912. These results indicated that the long side chain at the C-3 position might inhibit a close interaction between the receptor site and the substrate molecule, thereby leading to low-affinity binding.