Temperature measurements were taken from the retina-choroid, scleral surface, or bulbar conjunctiva in cats and monkeys. Decreasing choroidal blood flow by elevating intraocular pressure produced a decrease in ocular tissue temperature. Confirmation of choroidal blood flow changes was obtained by the hydrogen washout technique, an independent measure of blood flow. We conclude that ocular tissue temperature can be used as a semiquantitative index of choroidal blood flow, and, being noninvasive, has potential clinical application.