(1) Changes with age in the Young's modulus of elasticity of human lens capsule and Bruch's membrane have been determined. In lens capsule the modulus decreases with age whereas in Bruch's membrane it increases. (2) Changes with age in the hydraulic conductivity of the human lens capsule and Bruch's membrane have also been determined and again show opposite changes with age. In the former membrane the hydraulic conductivity increases while in the latter it decreases. (3) The ageing changes in the respective membranes indicate that, in man, some time after 100 years in all cases the lens capsule would have a similar hydraulic conductivity to lenses with advanced cataract, while in the same subject Bruch's membrane would have lost its permeability to water.