The method and device serve to measure a proportion of constituents in blood. To this end, electromagnetic radiation of different radiation wavelengths is directed through a tissue (9) containing blood vessels (1). At least a portion of the radiation exiting the vessel is detected using sensors, and a corresponding measured value derived therefrom is fed to an evaluating device. The evaluating device (10) is connected to at least two sensors (2, 3, 4) and has an analyzer (11) for determining a dispersion of radiation by evaluating the intensity of the radiation received by the individual sensors. An individual calibration determination is carried out by evaluating the angle-dependent dispersion and can be drawn upon for conducting a pulse spectroscopic determination of concentrations of substances.