The whole-cell mode of the patch-clamp technique has been used to monitor ionic currents in T84 colonic carcinoma cells. The cells were stimulated by either a cAMP cocktail, ionomycin or hypotonicity. Sizeable currents with distinct kinetics were observed after the stimulation with the different agonists. These kinetically distinct Cl⁻ currents also presented a differential sensitivity to the anti-oestrogen Tamoxifen and to the halide I⁻. Tamoxifen only inhibits the volume activated Cl⁻ current without affecting the other two. Substitution of extracellular Cl⁻ by I⁻ shifted the reversal potential towards more negative values both in the hypotonicity and ionomycin activated Cl⁻ currents. The cAMP activated current responded to the Cl⁻ substitution by I⁻ with a blockade of both outward and inward currents, in addition to the displacement of the zero current level towards positive values. Thus, the use of these two simple tools, I⁻ and tamoxifen, allows the distinction of Cl⁻ channels in epithelial cells.