GABA-immunoreactive (IR) neurons were observed in the accessory olfactory bulb (AOB) of adult female rats. Many somata and dendritic trees of periglomerular-located cells were GABA-IR and the size of their somata was variable. Numerous somata and dendrites in the granule cell layer were IR. These results suggest that a large number of the interneurons in the AOB are GABA-IR.