Men and women ages 18 through 79 diagnosed with diabetes mellitus and who had neovascularization on the optic nerve head (NVD) were eligible. NVD in one or both eyes of each patient had to be greater than or equal to DRS Standard Photograph 10A. NVD was defined as new vessels on the surface of the retina, further forward in the vitreous cavity over the disc, or within one disc diameter of the disc in any direction. Patient's ocular media must have been clear enough for fundus photography, which allowed the extent of neovascularization on the optic nerve head to be assessed. (If vitreous hemorrhage or other media opacity prevented adequate visualization of the neovascularization, it would greatly impair the ability to assess the effect of photocoagulation.) Another requirement for patient eligibility was the presence of an area of at least three quadrants of the retina in which full argon or krypton laser panretinal photocoagulation could be placed. (Vitreous hemorrhage and/or traction retinal detachment that interfered with treatment was less than one quadrant in extent.)