A method and apparatus for non-invasive determination of a measured variable of an analyte in a biological body. The body is irradiated locally by light in an automatic manner from a wavelength range matched to an absorption signature of the analyte. At least some of the light penetrates into the body and is absorbed by the analyte. The body heats up at least locally as a result of the absorption by the analyte and a consequently occurring change in a speckle pattern of coherent light scattered at the body is detected. A value of the measured variable of the analyte is deduced from the detected change in the speckle pattern. In particular, the concentration of glucose is established in a non-invasive manner as a measured variable.
