Experimental studies from our laboratory have suggested that single exposures to 5-fluorouracil (5-FU) would have a similar effect to subconjunctival injections of 5-FU and a less permanent effect on subconjunctival fibroblasts than mitomycin C (MMC). Thirty four eyes of 33 glaucoma patients with an increased risk of filtration surgery failure were treated with a single intraoperative 5 minute exposure of sclera and subconjunctival tissues to 5-FU, 25 mg/ml. The follow up period ranged from 3-9 months, during which two high risk eyes failed completely and one required topical beta blockers to control intraocular pressure. No low/moderate risk eyes failed. Single 5 minute intraoperative exposures to 5-FU are convenient, inexpensive, have no significant corneal side effects, and may be a useful adjunctive treatment to optimise the results of glaucoma filtration surgery, particularly in the large group of low/moderate risk patients.