The geometry of the cortex and nucleus of excised human lenses was determined by photography and dissection. Samples of the cortex and nucleus were measured spectrophotometrically to allow determination of light loss through the whole lens and the light loss per unit pathlength. It was concluded that the reduction of short wavelength light transmission with increasing age is due to two processes; first, the nuclear pathlength remains constant but there is increased pigment deposition; second, the pigment concentration does not change in the cortex but the pathlength increases.