Potassium channels play a major role in determining the pattern and frequency of neuronal firing. In the cochlear nucleus (CN), various morphologically defined types of neurons have different responses to a sound. We have previously identified one type of cloned K+ channel, termed Kv3.1, which is highly expressed in many auditory neurons. Expression studies indicate that Kv3.1 channels have an unusually high threshold for activation. In this study, we used both in situ hybridization and immunohistochemistry to examine the expression patterns of the Kv3.1 channel in the CN. In the ventral CN, bushy cells hybridized strongly with Kv3.1 specific probes and a subpopulation of stellate/multipolar cells hybridized with Kv3.1 probes. In the dorsal CN, pyramidal and large multipolar/giant cells expressed Kv3.1 mRNA. Abundant Kv3.1 immunolabeling was also observed in the CN. The pattern of immunolabeling revealed that the Kv3.1 protein is distributed along the soma, proximal dendrites, unmyelinated axons, and axon terminals of stained neurons. In the case of pyramidal and octopus cells, no immunolabeling was detected at the somata, even though these cells expressed Kv3.1 mRNA. Computer simulations were used to explore the functional role of the Kv3.1 channel. The simulations indicate that Kv3.1 conductances may contribute to repolarization of large synaptic potentials. When stimulated at high frequencies, the presence of Kv3.1 enhances the ability of a model cell with some of the features of bushy cells to follow high frequency input with temporal precision.