The invention relates to a method and a sensor for measurement of tissue perfusion. The sensor is provided with a reservoir (4) for a fluid or gaseous tracer and a tracer-permeable barrier (3), a sub-surface of which is in contact with the surrounding tissue and another sub-surface of which is in contact with a detection cavity (5) which is connected to a suitable apparatus for the measurement of tracer concentration in the detection cavity. The concentration of the tracer in the detection cavity is a measure of perfusion in the surrounding tissue. According to another embodiment of the invention it is also possible to carry out measurements of perfusion in the surface layers of the skin or of an organ.