Abstract: The deformability measurement chamber is subdivided by a foil into two chamber spaces. The foil has a passage opening, the diameter of which is smaller than the diameter, at rest, of a red blood corpuscle. A static pressure gradient exists between the two chamber spaces, so that a flow takes place from one chamber space to the other. In the region of the passage opening there is situated on each side of the foil an electrode, which is connected to an alternating voltage source. In order to achieve a measurement signal which is approximately one order of magnitude greater, at a given alternating voltage frequency, a current-measuring operational amplifier is disposed in the connecton of one electrode to the voltage source.