The Ussing chamber technique is a simple, but powerful technique to investigate ion transport. Originally designed to study vectorial ion transport through the frog skin, it has revolutionized our knowledge about how eletrolytes permeate epithelia. Here we discuss the physiological principles that underlie the technique and protocols to investigate the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in transepithelial ion transport.