The hydrodynamic properties of isolated human Bruch's membrane and choroid were investigated as a function of age and retinal location. Macular and peripheral regions of the fundus showed an exponential decline of hydraulic conductivity with half-lives of 15 and 22 years respectively. Comparison of age profiles for hydraulic conductivity and lipid deposits suggests the involvement of two discrete processes for reduction in transport capability. The first appears to involve 'membrane remodelling' with a programmed decay rate leading to a major reduction in hydraulic conductivity by the fifth decade of life. The second commences in the fourth decade and is apparently dependent on the lipid content of Bruch's membrane.