It has been shown that ionic conductance of the fundic area of gastric mucosa is via the cellular route, whereas in the antrum, conductance is by a shunt or paracellular pathway, using a variety of microelectrode techniques. Definition of the nature of the fundic conductance pathways has shown them to be largely neutral fixed-site (channel) ionophores of varying ion selectivity. Extraction of highly purified membrane fractions produces three separable channels-a cation, an anion and a non-selective channel, as measured after incorporation into an artificial bilayer. A model for proton transport, involving an electrogenic HCO3- ATPase pump shunted by a Cl- channel, is discussed. © 1973.