The invention relates to an apparatus and method to determine and monitor the flow rates and volume of fluids excreted or secreted by the body.The invention achieves the above objects by providing an apparatus comprisinga measuring unit comprising a conduit made of a material having a low thermal conductivity and supporting at least two thermistors an upstream thermistor serving as a compensation thermistor and a downstream thermistor located as far downstream as possible from said upstream thermistor and pre-heated to and kept at pre-defined temperature which is warmer than the fluid temperature to be metered andmeans for applying small electric voltages to the thermistors to enable generation of an electric signal anda control and display unit being operatively connected to the measuring unit.
