Electrophysiologically, astrocytes are characterized by a high K(+) resting conductance and a hyperpolarized resting membrane potential. Both features are due to the activity of astrocytic potassium channels. Astrocytes express a variety of voltage-dependent and leak potassium channels on the plasma membrane that contribute to the hyperpolarized resting membrane potential and other cellular processes. This chapter focuses on measuring K(+) channel function in astrocytes, focusing on Kir4.1, an inwardly rectifying potassium channel. We and others have demonstrated that Kir4.1 contributes significantly to the high-resting K(+) conductance and the hyperpolarized resting membrane potential. This channel is also implicated in channel-mediated regulation of extracellular potassium.