A prospective, randomized, double-masked, and placebo-controlled study was performed to evaluate the effects of a localized and sustained release of mitomycin on the success of glaucoma filtration surgery in rabbits. A bioerodible polymer was used as the drug carrier. Full-thickness filtration surgeries were performed and data from 22 rabbits were collected. One eye received a polymer impregnated with mitomycin (0.02 mg or 0.06 mg), while the fellow eye received a drug-free polymer. Intraocular pressure, bleb survival, and postoperative complications were investigated. Intraocular pressures remained lower for a longer period of time (P less than 0.004) and filtration blebs lasted longer (P less than 0.05) in experimental eyes than in control eyes. Conjunctivitis and sectorial corneal haze occurred more frequently in eyes treated with the higher dosage mitomycin compared with control eyes. The use of mitomycin-C in a polymer delivery system appeared to promote the success of glaucoma filtration surgery in rabbits. With the lower dosage of mitomycin, clinically significant ocular toxicity was not noted.