In the cerebral cortex, the voltage-gated potassium channel, Kv3.1b, a splicing variant of Kv3.1, has been associated with fast-firing interneurons. Here, we report strong expression of Kv3.1b-protein and mRNA in both Betz and Meynert pyramidal cells of the monkey, as shown by immunohistochemistry and in situ hybridization. Strong expression also occurs in large pyramidal neurons in layer 5 of several cortical areas. In addition, most of these Betz and layer 5 pyramids, and about 10% of the labeled Meynert cells weakly co-expressed the calcium binding protein parvalbumin. Electron microscopy shows that the expression of Kv3.1b is localized to the somal and proximal dendritic cytoplasmic membrane, as expected for a channel protein. These results suggest that some large pyramidal neurons may constitute a functional subpopulation, with a distinctive distribution of voltage-gated potassium channels capable of influencing their repetitive firing properties.