Measurements of diffusion of bleaching agents showed that diffusion coefficients are in the range of 10⁷-10⁸cm²/sec. at temperature of 20°C to 40°C, depending upon the extent of hardening of gelatine layer. The activation energies were calculated to be ca. 3-6 Kcal/mole. Assuming that the gelatine layer was around 20μ in thickness, the concentration of bleaching agent throughout the layer should be attained to equilibrium with bleaching solution in the period of about 90 sec. of processing. It was, therefore, suggested that the over-all bleach processing speed of conventional color films might be greatly influenced by the diffusion rate of bleaching agent.