PURPOSE: The purpose of this study was to assess the effects of intraoperative mitomycin-C (MMC) on the function of Baerveldt glaucoma implants in rabbits. METHODS: Bilateral implantations of 200 mm2 Baerveldt drainage devices were performed in 30 normal albino rabbits. One eye, randomly selected, received intraoperative application of MMC at the site of the implant plate for 5 min, via a 6 x 4 x 2 mm cellulose sponge saturated with 0.5 mg/ml of MMC. The opposite eye served as a control. MMC-treated and control eyes (five animals each group) were compared for intraocular pressure (IOP), resistance to flow, flow rates through the implant and histopathological findings at 2, 4, 6, 12, and 24 weeks postoperatively. Resistance to flow and flow rates through the implants were studied after opening the cornea and connecting the drain tube to a micromanometric system. RESULTS: Preoperative IOP did not differ between groups. MMC-treated eyes had lower levels of IOP than did controls at all postoperative times. The differences in IOP were statistically significant up to 8 weeks postoperatively. Resistance to flow was lower in MMC-treated eyes at all times studied, but the differences were statistically significant only at the time points of 2, 4, and 6 weeks. Flow rates through the implant bleb were always higher in MMC-treated eyes, and statistically significant differences were seen at 2, 4, 6, and 24 weeks. Histopathologically, MMC-treated eyes had thinner implant capsules with delayed maturation and less inflammatory infiltrate. CONCLUSION: MMC causes lower IOP and higher perfusion rates through the implant capsule at 2, 4, and 6 weeks postoperatively. Wound dehiscence, bleb leaks, and extraocular muscle injury were observed only in MMC-treated eyes.