A brief review of some of the relationships between the secretory rate and the electrophysiological characteristics of the canine and frog gastric mucosa is presented. There is no simple relationship between the potential difference (PD) and H+ rate in the in vitro frog gastric mucosa with standard Cl- bathing solutions. In contrast, with Cl- -free solutions (PD is inverted) there is a precise linear relationship between the PD and the H+ rate. This linear relationship is strong support for the concept that the H+ mechanism under these conditions is electrogenic. In the past it has been difficult rigorously to exclude the possibility that the inverted PD is due to a liquid junction potential between acid fluid in the lumina and the secretory bathing solution. Use of aminopyrine or imidazole essentially eliminates the possibility that the inverted PD is due to a liquid junction potential. Hence the linear relationship is solid evidence for the electrogenicity of the H+ mechanism. Recently we have shown that aminopyrine or imidazole can reverse thiocyanate inhibition of H+ secretion.