Distribution of the enzyme monoamine oxidase B (MAO-B) and the peripheral benzodiazepine binding site (omega 3 site) was studied by quantitative autoradiography using [3H]L-deprenyl and [3H]PK 11195, two tentative glial markers, as ligands. Sclerotic hippocampus from seven patients who had had anterotemporal lobe resection because of intractable complex partial epilepsy were investigated and compared with postmortem hippocampus from three nonepileptic controls. A significantly higher degree of L-deprenyl and PK 11195 binding was observed in the epileptic cases. The increased binding of both ligands correlated to extent of neuronal loss, but only PK 11195 showed correlation to degree of gliosis. We concluded that both ligands could provide useful markers for quantitating the degree of gliosis in pathologic states such as epilepsy. They may be applicable in future in vivo studies with positron emission tomography (PET).