A method for the analytical determination of the glucose concentration in a biological sample. In a detection step, light is irradiated into the sample and the light emerging therefrom after interaction with the sample emerges therefrom is detected in order to measure a physical light property affected by said interaction. The glucose concentration is determined from this measurement in an evaluation step. To provide a method for determining glucose in reagent-free and non-invasive manner, the invention proposes that a portion of the light emitted by the light source be guided along a reference light path of defined optical path length to the photodetector, that the total measuring light path also has a defined optical length and that the measuring light path after it has traversed the sample is so combined with the reference light path that the measuring light and the reference light interfere with each other. The photodetector measures an interference signal used in the evaluation step to determine the glucose concentration.