Abstract: The chamber for treating cells in an electric field includes an interior ce for a cell suspension having a region between the electrodes inside of which the cells are exposed to the electric field. In order to provide an improved chamber the region in which the cells are treated--up to an inlet or outlet for the cell suspension--is bounded by surfaces of the electrodes which are positioned equidistant from each other. Preferable these electrode surfaces are coaxial or concentric. In one specific embodiment of my chamber a first electrode is the inner electrode and a second electrode is the outer electrode and the surfaces of the inner electrode and the inside surfaces of the outer electrode are cylindrical so that the region between the electrodes is a cylindrical annular space.