During summer 2006, 9 supermodules of the CMS electromagnetic calorimeter (ECAL) have been exposed to an electron beam at the CERN SPS north area facility. Each supermodule contains 1700 crystals. The intercalibration coefficients of the different channels have been measured for each supermodule. The reproducibility of the intercalibration has been tested by measuring a supermodule twice. The intercalibration coefficients obtained in the electron beam have also been compared with those obtained with cosmic ray muons
