Our understanding of pH regulation has been studied in-depth in the endocytotic pathway of the cell because of fluid phase and membrane-bound pH-sensitive markers that could be delivered and taken up exogenously by the cell (1 ,2 ). Very little is understood, however, about the ionic composition of the two major compartments of the secretory pathway, the Golgi complex and the endoplasmic reticulum (ER). This has been largely the result of the relative inaccessibility of these compartments to exogenous probes, as the favored direction of flow of membrane and fluid-phase components in the secretory system is in the exocytotic direction.