The course of development of light dissemination was investigated for rat lenses exposed in vivo to 30 kJ/m<sup>2</sup> ultraviolet radiation (UVR) in the 300-nm wavelength region After an initial latency phase the light dissemination increases rapidly. At 72 h after the exposure to UVR, light dissemination almost reaches a maximum. An exponential model is proposed for the analysis of this pattern. Light dissemination also increases in lenses contralateral to exposed. This indicates that there may be a systemic reponse after exposure to UVR which can lead to cataract formation.