A voltage-dependent outward KC (Kv) current in the intermediate cell (melanocyte) of the cochlear stria vascularis was studied using the whole cell patch-clamp technique. The Ky current had an activation threshold voltage of approximately -80 mV, and 50% activation was observed at -42.6 mV. The time courses of activation and inactivation were well fitted by two exponential functions: the time constants at 0 mV were 7.9 and 58.8 ms for activation and 0.6 and 4.3 s for inactivation. The half-maximal activation time was 13.8 ms at 0 mV. Inactivation of the current was incomplete even after a prolonged depolarization of 10 s. This current was independent of intracellular Ca2+. Quinine, verapamil, Ba2+, and tetraethylammonium inhibited the current in a dose-dependent manner, but 4-aminopyridine was ineffective at 50 mM. We conclude that the Ky conductance in the intermediate cell may stabilize the membrane potential, which is thought to be closely related to the endocochlear potential, and may provide an additional route for K+ secretion into the intercellular space.