The spectral-sensitization of an AgCl emulsion was investigated in the presence of some fog inhibitors. It was found that the sensitivity of spectral-sensitized emulsions could be increased or decreased by these inhibitors according to the order of addition of the compounds. On the basis of spectral measurements, one reason could be the influence of these compounds on the aggregation behavior of the cyanine dyes. When it was beneficial to the formation of dye J-aggregates, sensitization took place; and when it was beneficial to the formation of dye H-aggregates, desensitization appeared. ESR experiments show that the addition of inhibitors can decrease the number and accelerate the decay of dye positive holes. The desensitization, caused by the recombination of dye positive holes with photoelectrons and/or latent image centers, was reduced in the presence of these fog inhibitors, leading to an increase in sensitivity of the emulsion.