Studies on the mechanism of desensitization by dyes have been mainly done by use of chemically unsensitized emulsion in the past, and revealed that (1) retardation of development, (2) electron trapping, and (3) hole trapping by dyes were the main causes for the desensitization by dyes. On the other hand, we have proposed a new mechanism for the desensitization by a cyanine dye in sulfur-sensitized cubic AgBr emulsion, according to which the desensitization is caused by enhancement of dispersion of latent images by dyes. The effect of sulfur-sensitization upon the processes of spectral sensitization is also discussed in this paper.