The light output response of CsI(Tl) scintillators, photodiodes readout, has been investigated for heavy ions with atomic number 3⩽ Z⩽54 for energies up to 45 MeV/u. The detectors have been calibrated with particular attention to the dependence on the atomic number of the ions. The expression obtained with this procedure was applied to the calibration of the CsI(Tl) detectors of the MULTICS array, on the basis of only one renormalization coefficient. A complete compatibility has been found with recent data at energies up to 60 MeV/u.