Contrary to IR spectra there are only very few or no maxima in most UV spectra. Therefore library search based on peak tables will not be successful. The use of derivatives seems insufficient for there are too less data points for numerical derivatives and in case of trace analysis the signal-to-noise ratio is too bad. Integral numerical values are proposed as mean absorbance in selected wavelength ranges (200–400, 200–300, 200–260 nm) as characteristics for information ranges in the wavelength domaine. On the other hand, the absorbance domaine is characterized by the cross correlation of the spectrum in the same wavelength ranges. These numerical values will differentiate also very similar spectra as carbromal, ephedrin, pethidin, lidocain and atropin, showing only end absorptions up to about 240 nm.