By reducing the dose of injected fluorescein its leakage from conjunctival and episcleral capillaries has been minimised. These vessels have been demonstrated with great clarity, and the venous circulation, previously obscured by extravascular fluorescein, has also been revealed. The anatomy of the anterior segment vessels, and the blood flow within them, has been studied in eight normal subjects. The anterior ciliary arteries feed an anterior episcleral arterial circle that has superficial and deep components. This supplies the anterior conjunctival and episcleral circulations, the limbal arcades, and the iris arterioles. Where the superficial arterial circle is deficient, isolated vessels emerge from the deep segments of the circle to supply the episcleral plexus and conjunctival arterioles. Watershed zones between the anterior and posterior territories of the conjunctival and episcleral circulations overlap. They may fluoresce up to 30 seconds after the anterior ciliary arteries. The scope of this technique and the implications of these findings are discussed.