Abstract: The invention relates to a method and a microsensor for measurement of transport coefficients like diffusivity or flow velocity. The microsensor has a reservoir provided with a mouth and a transducer. The transducer has a tip placed in the mouth, which can be provided with a membrane or insert. The reservoir contains one or more gases or one or more liquid-dissolved substances intended for the diffusion through the mouth into an area or field of a medium outside the mouth of the reservoir. The transducer measures the partial pressure of the gas or the concentration of the liquid-dissolved substance in the mouth, whereby transport coefficients of diffusivity or flow velocity are determined. Preferably, the gradient of the partial pressure or the concentration is determined.