Calcium-binding proteins, such as parvalbumin (PV) and calbindin (Calb), are commonly used as markers for classifying inhibitory interneurons into subgroups in neurbanatomical studies. PV-immunoreactive neurons are involved in the generation of gamma oscillations, which regulate working memory and information transmission between cortical areas. Here the authors investigate the two populations of inhibitory interneurons in the hippocampus by using immunohistochemistry. While PV-immunoreactive neurons distribute sparsely with plenty of dark neuritis, Calb- immunoreactive neuronswere slightly stained with less neurites. Calbindin was not only positive to interneurons, but also pyramidal neurons which indicate its non-specificity.