The invention relates inter alia to a method for measuring the oxygen saturation of the blood flowing in a peripheral human or animal body part (20), in which electromagnetic radiation (q1′(t), q2′(t)) having a first and a second wavelength is irradiated into the peripheral body part or irradiated through the peripheral body part, the reflected or transmitted radiation (x1′(t), x2′(t)) is measured to form two measurement signals (x1(t), x2(t)), and the oxygen saturation of the blood is determined by evaluating the two measurement signals. According to the invention, provision is made for a mathematical mixing model to be used to evaluate the two measurement signals and a statistical evaluation method to be applied to the two measurement signals, wherein, as a boundary condition, the statistical independence of a useful source signal and an interference source signal is assumed and the useful source signal and the two useful-signal-related filter functions are determined with the aid of the evaluation method and the oxygen saturation of the blood is determined using the three aforementioned signals.