The patch clamp technique enables the analyses of various ion channel characteristics of individual cells in vitro. The most important difference from previous techniques is that the microelectrode (pipette) is firmly attached to the cell surface instead of being inserted into the cells, and the so-called "giga-ohm seal" is attained. Usually, the whole conductance of the cell membrane is measured under "whole cell" and "perforated patch" modes, whereas single channel recordings are also possible by employing relevant modes such as the "cell attached" mode. In the most frequently used "whole cell" mode, the intracellular potential (voltage clamp) or the whole cell current (current clamp) can be kept constant, since the leakage current is very small. Exemplary recordings are also shown from the author's experiments.