Experiments have been performed in order to assess whether the antisecretory factor (ASF) can influence the permeation of Cl- ions across the Deiters' neurone plasma membrane in the outward direction. ASF is a naturally occurring, acidic protein with a molecular weight of about 60,000, which specifically inhibits enterotoxin-induced intestinal secretion. Both basal and "intracellular" GABA activated Cl- permeability was studied, and the result confirmed the existence of GABAA receptors on the Deiters' membrane cytoplasmic side. ASF completely abolished the effect of "intracellular" GABA on Cl- permeability in the outward direction. However, ASF did not influence the basal Cl- permeability in the outward direction.