1. The short duration cerebrovascular perfusion method for measuring permeability of the blood-brain barrier has been adapted to measuring transport into the retina. 2. The method has been characterized on the one hand by comparing uptakes of radiotracers during HCO3(-)-buffered saline perfusion with those occurring after intravenous bolus injection of radioisotopes, and on the other by comparing uptake into retina with the uptake into frontal cerebral cortex. The mean permeability-surface area (PS) products (ml s-1 g-1) for [14C]urea and [14C]thiourea in the perfused retina were 1.2 +/- 0.26 x 10(-3) and 2.1 +/- 0.01 x 10(-3) respectively. The intravenous injection method gave comparable values for [14C]urea and [14C]thiourea of 1.6 +/- 0.28 x 10(-3) and 3.24 +/- 0.55 x 10(-3). The rates of uptake of the hydrophilic solutes were 2- to 7-fold greater than in brain. 3. Retinal and choroidal capillary perfusion fluid flow rates were measured using a diffusible flow marker ([14C]diazepam) and a particulate indicator (15 microns cerium141-labelled microspheres). Results using both flow markers confirmed that both capillary networks supplying the retina were being adequately perfused.