A probe (1) for measuring the oxygen content in a biological material, with an oxygen-sensitive dye located on a distal end face of an optical fiber (2), comprising a distal fiber section inclusive of the distal end face along with the dye enclosed by an oxygen-penetrable, fluid-impenetrable membrane (7), which in the enclosed area provides a gas space (8) encompassing the distal end face with the dye, where the thickness of the membrane where it creates the gas space is uniform, is new. An independent claim is included for a catheter (14) with the probe, and a temperature sensor (30) for measuring the temperature of the biological material encompassing the catheter, and preferably a pressure sensor (28) measuring the pressure.
