This chapter discusses various techniques used for the study of ion and water transport mechanisms in isolated Necturus gall bladder epithelium.With appropriate modifications, these methods can be applied to other epithelia as well as to non-epithelial preparations. The emphasis is on techniques, but this chapter also has attempted to provide orientation for the non-specialist on the rationale of the experimental approaches utilizing these methods. This chapter also illustrates the application of each technique in identifying and characterizing mechanisms of ion and water transport across individual cell membranes, and their regulation. Compared to other methods, electrophysiological techniques have major advantages in both accuracy and time resolution, and permit measurements in a nondestructive fashion. Conventional intracellular microelectrodes are used in epithelial transport studies to measure cell membrane voltages, electrical resistances, and ion selectivities. This chapter concludes with the brief discussion on electrophysiologic apparatus.