Fluorescein angiography of the angle with the Goldmann gonioscopy lens was used to examine eyes of 100 Japanese patients with diabetes mellitus. Ocular tension was 21 mmHg or over in 31 of these 100 patients. Gonioscopy revealed angle neovascularisation in the eyes of 30 patients; however, fluorescein gonioangiography showed evidence of angle neovascularisation in 56 of the 100 patients. Angle neovascularsation was first seen 20.3 +/- 4.1 s after injection of fluorescein dye. Of the newly formed vessels, the branching small vessels showed more prominent leakage than the larger vessels at the root. With progression of the retinopathy, angle neovascularisation became more severe. Following panretinal photocoagulation in 26 of the patients with neovascular glaucoma, angle neovascularisation remarkably regressed in 12 and moderately regressed in 7 patients. Ocular tension became normal in 13 patients. Two of 31 patients with ocular hypertension were considered as cases of primary open-angle glaucoma as there was glaucomatous cupping, visual field defects and no evidence of newly formed vessels in the angle, as observed using fluorescein gonioangiography. Thus, fluorescein gonioangiography may be helpful in the diagnosis and clinical management of neovascular glaucoma.