Although microelectrode measurements have caused a good deal of confusion in the investigation of renal electrolyte transport (for literature see Ref.4), we cannot do without them. Knowledge of the electrical potential steps, which the ions have to pass during their reabsorption, is indispensable for understanding the transport mechanisms involved. Hence the development of more reliable methods to measure the electrical properties of kidney tubules was an important as well as challenging problem. This paper deals with some of the advances effected in our laboratory in the past 5 years. The properties of microelectrodes that present the major problems are: 1. The invisibility of the electrode tip, 2. The instability of the tip potential, and 3. The instability of the tip resistance. Since a brief description of resistance measurement problems has been published elsewhere recently (14), only the first two points will be discussed here. Simple microscopic observation alone can never tell whether the invisible microelectrode tip has penetrated the invisible cell membrane. In order to decide whether the tip sticks within a cell or whether it has reached the tubular lumen a number of localization methods have been developed.