During osmotic swelling of a human intestinal epithelial cell line, stepwise closing unitary events of Cl- channels could be observed in cell-attached patches upon application of large positive potentials only when inactivating whole-cell Cl- currents were simultaneously observed. The closing process became faster with increasing positive command pulses. The unitary conductance was around 32 pS at 60 mV, 37 pS at +100 mV, and 47 pS at +140 mV exhibiting outward rectification.