By patch-clamp analysis of lipid supplemented vesicles prepared from the sarcolemma of mouse wildtype skeletal muscle, we could identify two known types of potassium channels, the inward rectifier and Ca2+ activated BK channels, and five types of chloride channels designated CIC-a, CIC-b, CIC-c, CIC-d, and CIC-e. CIC-b corresponds to a known chloride channel, whereas CICa, -c, -d and -e have not been described previously. The diversity may be due to a heterooligomeric composition of different subunits. None of these chloride channels nor the potassium channels were found in the sarcoplasmic reticulum fraction. In vesicles from myotonic mice, Clc-d and -e were not found.