Two types of benzodiazepine binding sites for [3H]diazepam in mammalian central nervous tissue were identified using selective in vitro tissue culture and in situ kainic acid lesion techniques. These two binding sites were pharmacologically distinguished by differential displacement of the [3H]diazepam radioligand using the centrally active benzodiazepine, clonazepam, and the centrally inactive benzodiazepine, RO5–4864. Clonazepam-displaceable binding sites were found to be located principally on neuronal membranes, while RO5–4864-displaceable binding sites were found to be located on non-neuronal elements. These pharmacological distinctions can be used to characterize the predominant cell types which bind benzodiazepines in nervous tissue. It is suggested that one quantitative measure of different cell populations is the ratio of clonazepam- to RO5–4864-displaceable [3H]diazepam binding within a single neuronal tissue simple.