A process for on-line and in situ counting of cells in a biological culture medium, comprising the following steps: a plurality of measurements of the capacitance of the medium or a plurality of measurements of the conductance of the medium, at distinct frequencies varying within a predetermined range of measurement frequencies, an extraction of information on the variation of permittivity due to the .beta.-dispersion in the medium, from the capacitance measurements, and processing of the variation of this information on the variation of permittivity as a function of the frequency, in order to provide information regarding the counting of cells in the medium.