Values of the diffusion coefficient into the anterior chamber and the blood aqueous barrier permeability as a function of age were determined by fluorophotometry in 58 healthy volunteers. The diffusion coefficient was calculated from aqueous fluorescein concentration and the time integral of non-protein bound fluorescein concentration in plasma. Blood-aqueous barrier permeability was calculated using diffusion coefficient values, the area of fluorescein inflow into the anterior chamber and anterior chamber volume. Values for diffusion coefficient as well as permeability were found to be independent of age between 13 y and 72 y (lin. corr. coeff. 0.2, p = 0.11) mean values were 4.7 .10(-4) min-1 +/- 1.5. 10(-4) SD and 15.4 nm/s +/- 4.8 SD, respectively. The difference between permeability values calculated from fluorophotometric scans at 30, 55 and 65 mins. after fluorescein injection was less than 5% and the 7 months reproducibility was within 15%. There was no significant correlation between simultaneously measured values of blood-retinal and blood-aqueous barrier permeability (lin. corr. coeff. 0.13, p = 0.4).