A microscale sensor for fluid velocity measurements has been developed and its properties investigated. The sensor can be made with tip diameters below 10 microns and the fluid velocity detection limit can be down to 5 microns/second. The sensor consists of a slim transducer (e.g. a gas microsensor) surrounded by a tracer gas reservoir in the form of a tiny glass tube. The tip of the tracer reservoir is closed by a silicon membrane that is penetrated by the transducer tip. The tracer gas diffuses out through the tip membrane and the concentration build-up at the tip is measured by the transducer. As the tracer build-up is a function of the fluid velocity at the sensor tip, the transducer signal becomes an inverse measure of fluid velocity. The tracer gas can be selected from a range of substances depending on the suitability in the relevant situation. For instance, in systems where the oxygen concentration is high or variable, acetylene can be used as a tracer along with an acetylene transducer, whereas in systems where long-term stability is important and where the oxygen concentration is not variable, oxygen can be used as a tracer, as the oxygen transducer is very long-term stable. The sensor tip is sharpened such that it can penetrate tissue without tearing it. This means that the sensor tip can be inserted into small biological channels, e.g. blood vessels and kidney tubules, without damage to the channel wall, making it a unique tool for investigating fluid velocities at very low velocities. There are alternative methods for measuring flow velocity (e.g. Laser-Doppler techniques and particle imaging systems), but these are inferior to the technique presented here with respect to velocity sensitivity (Laser-Doppler) and spatial resolution (imaging). The sensor signal is acquired with picoammeter technology and the positioned with positioning equipment, both of which are readily available.