Application of the conventional whole-cell patch-clamp method leads to a replacement of the intracellular fluid with the intracellular pipet solution. The speed of this replacement or dialysis depends on the cell volume and electrode tip diameter. Although this mechanism can be used advantageously in many experiments, there are conditions where such a dialysis interferes with the current response to be tested. The response will disappear sometimes within minutes, an event that is usually called “rundown.” Several strategies have been developed in the last 10 yr to overcome this rundown. The most successful use nystatin or amphotericin B in the pipet. These, are ionophores that decrease the resistance of the sealed patch of membrane to selected small ions. A breaking of the patch membrane is not involved. Using such a principle, Lindau and Fernandez (1986) conducted experiments using ATP to permealize the patch membrane. ATP is, however, of limited use because it is dependent on a receptor. A breakthrough was the use of nystatin, first introduced by Horn and Marty (1988); this drug is an ionophore that is receptor-independent. A further improvement was the introduction of amphotericin B by Rae et al. (1991).