It is well known that thiocyanate inhibits gastric secretion. We review the results of experiments based on an hypothesis for its inhibitory action. An aspect of gastric secretion that has challenged investigators from the time of Claude Bernard has been the site of hydrogen formation. A large amount of work involving the use of pH indicators seemingly supports the concept that the gastric cells secrete a neutral precursor and that hydrochloric acid is formed on the surface of the stomach. A fallacious assumption has been made in the interpretation of these studies. Other studies on the mechanism of water transport lead to the conclusion that H+ and CI are present as such in the tubular and canalicular lumina and together with water are secreted by the tubular cells.