Abstract: A process and apparatus for flow measurement in which a marker volume is generated by the application of an electric voltage. This marker volume runs through a measured length in the direction of flow. The flow speed or a measurement linked to the flow speed is calculated from the transit time of the market volume. In adapting same for use in the characteristic flow range of body-related, aqueous fluids, that is, for measuring the flow of electrolytic, body-related fluids, the marker volume is generated by a short-term electrolytic breakdown of the fluid and the applied voltage is less than 24 Volts.