Glucocorticoid-induced cataracts in chick embryos were monitored by an image analysis system. Opacities in the lens visually showed a complex pattern with significant changes in the cortical and nuclear regions. An electronic image analyser produced an image in which contrast represented different zones of lens opacification in the frontal plane and documented objective lens findings such as the precise topography of the opacities, density and opacity measurements, geometric measurements of boundary surfaces and of regional areas. Parameters of lens clouding were evaluated quantitatively by measuring the optical density index and the area of the zones of clouding outlined with equi-densities. The light intensity standard graded different morphological areas of the lens into up to 256 grey levels. The data were entered and stored quantitatively into a computer. The lens images thus picked up by the TV camera and digitally stored in a frame buffer of the measuring system could be reliably transformed into a 2-D or 3-D picture of lens clouding. The approach demonstrated by the current study provides a sensitive and meaningful measure of cataractous changes for lens laboratory research.