Cell-attached recordings revealed Cl^- channel activity in basolateral membrane of guinea pig distal colonic crypts isolated from basement membrane. Outwardly rectified currents (^gpCl_or) were apparent with a single-channel conductance of 29pS at resting membrane electrical potential; another outward rectifier with of 24pS also was observed (~25% of ^gpCl_or). At a holding potential of -80mV was 18pS for both ^gpCl_or, and at +80mV was 67pS and 40pS, respectively. Identity as Cl^- channels was confirmed in excised patches by changing bath ion composition. From reversal potentials, relative permeability of K⁺ over Cl^- (P_K/P_Cl) was 0.07±0.03, with P_Na/P_Cl=0.08±0.04. A second type of Cl^- channel was seen with linear current-voltage relations (^gpCl_L): subtypes with of 21pS, 13pS and 8pS. Epinephrine or forskolin increased the number of open ^gpCl_or and ^gpCl_L. Open probabilities (P_o)of ^gpCl_or, ^gpCl_L21 and ^gpCl_L13 were voltage-dependent in cell-attached patches: higher at more positive potentials. Kinetics of ^gpCl_or were more rapid with epinephrine activation than with forskolin activation. Epinephrine increased P_o at the resting membrane potential for ^gpCl_L13. Secretagogue activation of these Cl^- channels may contribute to stimulation of electrogenic K⁺ secretion across colonic epithelium by increasing basolateral membrane Cl^- conductance that permits Cl^- exit after uptake via Na⁺/K⁺/2Cl^--cotransport.