The invention relates to a probe for measuring the biomass content in a medium having a suspending fluid and cells. The probe has at least three electrodes, wherein two of the electrodes are configured as excitation electrodes for transmitting an excitation signal through a medium. Two of the electrodes are configured as signal electrodes for receiving an excitation signal that has passed through the medium. The or each signal electrode is located between the two excitation electrodes at a position where a high current density is generated. The probe can have two excitation electrodes and four signal electrodes. The signal electrodes are configured substantially in parallel and arranged in couples adjacent each other, at positions between the excitation electrodes. The signal electrodes are configured such that (i) a first couple of signal electrodes are arranged between the closest end points of the excitation electrodes at one side of the probe, and (ii) a second couple of signal electrodes are arranged between the closest end points of the excitation electrodes at the other side of the probe.