THE retinal vascular system has long been of interest to both clinicians and basic scientists because of its involvement in a number of systemic diseases, particularly hypertension and diabetes mellitus, and its accessibility to in vivo study through direct observation due to the transparency of the eye. This accessibility has made it an ideal system for the study of a portion of the microcirculation in various physiological and pathological states as well as under the influence of pharmacological agents. Such studies have advanced considerably the clinical and experimental investigation of retinal vascular disease which is one of the most common causes of visual disturbance and blindness in man. But in vitro study of retinal blood vessels has been restricted largely to the examination of retinal digest preparations obtained with the use of proteolytic enzymes1 or by autolysis of the retina in water2, and of isolated vessels obtained by microdissection techniques3. Metabolic studies on such preparations of isolated vessels have been extremely limited3 because of the non-physiological conditions used or their tedious and time consuming nature. Therefore, we have developed a simple procedure for the isolation of a purified preparation of bovine retinal vessels which are metabolically active. © 1974 Nature Publishing Group.