The unique anatomical and functional properties of the eye present formidable obstacles in the development of a reliable, accurate method for measuring ocular blood flow. Recent refinements in concepts and techniques for estimating regional blood flow in other tissues have considerable potential for resolving several of these obstacles. The advent of nuclide labeled microspheres of appropriate size to impact in the vascular bed has provided a nonrecirculating indicator of fractional distribution, permitting a direct reproducible technique for ocular blood flow measurement This report describes our preliminary observations on the use of radioactive microsphere in measuring total and segmental blood flow in rabbit and monkey eyes.