Anterior segment fluorescein angiography was performed on 135 patients with scleritis and episcleritis and on several normal subjects. It was confirmed that the coats of the eye anterior to the extraocular muscles derive their blood supply from perforating ciliary vessels. Characteristic patterns were detected which could distinguish the various forms of scleritis and episcleritis. Fluorescein angiography was found to be particularly useful in the detection of those patients who have early, but not clinically recognisable, necrotizing scleritis. The fluorescein angiographic appearances have been used to help to determine whether treatment should be given with nonsteroidal anti-inflammatory drugs, with systemic steroids or other immunosuppressive agents.