Abstract: A method of determining at least the concentration of a component from the intensity of electromagnetic waves with at least two selected wavelengths which are reflected by human tissue or transmitted through human tissue comprises firstly the step of converting the intensities of the received electromagnetic signals into at least one first and one second time-dependent electric signal. Then a time-discrete transformation of the first and of the second electric signal into the frequency domain is performed to determine first and second spectral values of the first and of the second signal. Complex combinatorial values are formed from said first and second spectral values and physiologically relevant combinatorial values are selected by evaluating the complex combinatorial values according to given criteria for the physiological relevance thereof. Finally, the concentration of the component is calculated by using the selected combinatorial values or by using the frequencywise-associated spectral values.