Transient potassium currents of the A type are thought to be important in a number of physiological processes of excitable cells, including spike repolarization and synaptic integration. This functional diversity may reflect the contribution of distinct subtypes of A channel to cellular behavior. Using the whole-cell variant of the patch clamp technique, we have found that two types of A-current are expressed in rat neostriatal neurons, one that is similar to previous descriptions in mammals and a second that is activated at considerably more depolarized potentials.