Chloride-selective ion channels were measured from isolated rat liver nuclei. Single ion channel currents were recorded in both "nuclear-attached" and in excised patches in the inside-out configuration of the patch-clamp technique. Two types of chloride conductance were defined, a large conductance (150 pS; iCl,N) channel with complex kinetics and multiple substates, and a second smaller conductance (58 pS;ICln) channel sensitive to block by ATP. The channels were inhibited by pharmacological agents known to block chloride channels and were insensitive to internal and external changes in calcium and magnesium. Presumably the channels reside in the external membrane of the nuclear double membrane and may mediate charge balance in the release and uptake of calcium from the perinuclear space.