  We present a method to measure the relative spectral response of the Pierre
Auger Observatory Fluorescence Detector. The calibration was done at
wavelengths of 320, 337, 355, 380 and 405 nm using an end-to-end technique in
which the response of all detector components are combined in a single
measurement. A xenon flasher and notch-filters were used as the light source
for the calibration device. The overall uncertainty is 5%.
