Under the double-patch configuration, stepwise closing unitary events could be observed in the on-cell patch upon applications of large positive potentials only when inactivating whole-cell Cl- currents were simultaneously observed in cultured human epithelial cells (Intestine 407) after osmotic swelling. Under the cell-attached configuration, the single channel events exhibited similar time- and voltage-dependent inactivation upon large depolarizations. The inactivation time course became shorter with increasing positive command pulses. The unitary slope conductance was around 63 pS at +140 mV and 46 pS at +100 mV exhibiting outward rectification.