Most of the thermoluminescence measurements on alkali halides, reported in the literature, correspond to the samples exposed to ionizing radiations. In analysing these measurements, it had been most often assumed that the number of filled traps equals the number of recombination centres, in this paper, glow curves and isothermal decay of TL is reported for KCI: Ca crystals which were electrolytically coloured to contain either F or V type centres prior to irradiation. The trapping parameters are obtained from these data and compared with those for the crystals which were exposed without subjecting to prior electrolysis. It was found that the apparent order of kinetics in the crystals containing excess V centres changed from one to two as the exposure increased from 0.36 to 21.6 C/kg. It was also found that the presence of excess V centres sensitized the thermoluminescence while that of F centres quenched the same.