A two-site enzyme-linked immunosorbent assay was used to quantitate levels of basic fibroblast growth factor in the vitreous from 36 patients undergoing vitrectomy for a variety of retinal conditions, including proliferative diabetic retinopathy, macular pucker, and retinal detachment with and without proliferative vitreoretinopathy. Basic fibroblast growth factor levels ranged from undetectable to 52 ng/mL. In patients with proliferative diabetic retinopathy, basic fibroblast growth factor levels were greater than or equal to 30 ng/mL in 8 of 17 specimens. Of the 8 patients with elevated basic fibroblast growth factor levels, 6 had evidence of active proliferative disease (ie, neovascularization of the disc or iris), whereas in the patients who had undetectable levels only 2 of 9 had evidence of neovascularization of disc and none had neovascularization of the iris. In the rhegmatogenous retinal detachment group, 2 of 10 eyes had elevated basic fibroblast growth factor levels, while none in the macular pucker group had elevated levels. Our study documents increased levels of basic fibroblast growth factor in vitreous specimens from patients with proliferative diabetic retinopathy, particularly those with active proliferative retinopathy. The role of basic fibroblast growth factor in the pathogenesis of various retinal disease entities is discussed.