A simple quantitative and reproducible method for evaluating lens transmission (lambda = 490 and 530 nm) is described. It is based on the measurement of autofluorescence in the anterior and the posterior part of the lens by means of a fluorophotometer, assuming an about equal fluorescence quantum efficiency in both parts. Consequently any difference in fluorescence between both parts can be attributed to a loss of exciting and fluorescent light in the lens. For both wavelengths, the average lens transmission is determined by this method in a normal population as a function of age.