Effects of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene (TAI) on the electronic properties of unsensitized and sulphur sensitized cubic AgCl emulsion grains were investigated by means of the Dember effect, and microwave photoconductivity. The results indicated that, in the presence of TAI, Dember photovoltage and its decay time and the lifetime of photoelectrons were increased, resulting from the decrease of the concentration of interstitial silver ions produced by TAI. The mechanism of sensitization by TAI suggested urns as follows: decrease of interstitial silver ions in silver halide grains by TAI modified the formation and the growth of primitive latent image centres, as well as the specks concentration process.