The patch-clamp methods were developed to investigate the ionic channels of cellular membrane. The methods and modes of patch-clamp study and the physiological role of voltage-dependent channels were briefly described in the text. The voltage-dependent channels of outer hair cells isolated guinea pig cochlea were investigated using patch-clamp technique in a whole-cell recording mode. Depolarizing voltage steps to potentials more positive than -30mV elicited a slowly inactivating outward K⁺ current (I_Kca), which is dependent on intracellular Ca²⁺. Hyperpolarizing voltage steps to more negative than -90mV rapidly inactivated an inward K⁺ current (I_{K, n}), which is already activated at resting membrane potential. When both K⁺ current were suppressed by replacing K+ with other cation of large molecule, depolarizing voltage steps elicited a slowly-inactivating inward current. The relations between this current and external Ca²⁺ concentration indicated that outer hair cell possesses L-type Ca²⁺ channel. The electrical model of outer hair cell in guinea pig cochlea was discussed in accordance to these results and the previous report by Housley and Ashmore.