  Most of the scientific instrumentation as well as the tracking systems and
the Shack- Hartmann wavefront analysers at the Italian National Telescope
Galileo use CCDs as detectors. The characterization of detectors is of
fundamental importance for their correct utilization in scientific
instrumentation. We report on the measurement of the electro-optical
characteristics of CCDs that will be used in the scientific instrumentation at
the Italian National Telescope. In particular we will show and compare the
quantum e{\AE}ciency, the charge transfer e{\AE}ciency, the dark current, the
read out noise the uniformity and the linearity of two sets of CCDs
manufactured by EEV and LORAL. Finally, we will show the preliminary tests done
at the telescope with the optical imager that has a mosaic of two EEV chips.
