1. The short-circuit current and absolute fluxes of Na+ and Cl- across the gastric mucosa of the 28-day rabbit foetus have been measured in vitro.2. Substitution of Na+ in the solution bathing the mucosal surface by choline ion or K+ resulted in a 70% decrease in short-circuit current which was reversed when Na+ was restored to the mucosal solution. The portion of the short-circuit current dependent on the presence of Na+ in the mucosal solution was found to be equivalent to the net flux of Na+ from mucosa to serosa.3. The net flux of Cl- from serosa to mucosa was compared with the short-circuit current persisting when Na+ had been replaced in the mucosal solution. Averaged results from sixteen experiments indicated that the net flux of Cl- was equivalent to 166% of the Na+ independent short-circuit current.4. The results indicated that the component of short-circuit current associated with acid secretion was independent of the presence of Na+ in the mucosal solution.5. The small scale of the experiments and the secretion of mucus by the preparation did not permit successful simultaneous measurement of H+ secretion and short-circuit current.6. Replacement of Cl- by SO42- or glucuronate in the solutions on both sides did not result in a reversal or decrease in magnitude of the Na+ independent short-circuit current, even after allowing time for the tissue to become depleted of Cl-. It is suggested that a non-specific active anion transport was occurring.
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