Filtering surgery adequately lowers intraocular pressure in most glaucoma patients. However, the prognosis is less favorable for aphakic patients with glaucoma or glaucoma in phakic eyes following unsuccessful filtering operations. Failure of filtering surgery is usually attributed to the proliferation of fibroblasts at the filtering site. The use of 5-FU, an antimetabolite, has been shown to inhibit the proliferation of fibroblasts in tissue culture, and in preliminary studies it has increased the success of filtering surgery in a nonhuman primate model.