The electrical resistance and the flow of solution in glass microelectrodes has been studied as function of the concentration of internal and external solution (KCl, 3–10−5 M), and as a function of pressure between the inside and outside solutions. The study demonstrates the usefulness of using microelectrodes for measuring cell membrane resistance and also the dangers in using them as microejectors because of anomalous flow effects. Electrokinetic effects and tip potentials are briefly described; they offer a means of investigating the surface condition of the glass wall inside the tip of the electrode and its variation with the outside solution.