The aim of the study was to evaluate the effect of mitomycin-C (MMC) in a second antiglaucoma operation after failure of the first operation. We assessed 46 patients (26 male, 20 female, mean age 64.2 years) with high intraocular pressure (IOP) (mean 32.4 +/- 5.2 mmHg) despite previous trabeculectomy (Tr-Ec) one to three years earlier and topical or systemic medical treatment. All patients underwent a second Tr-Ec and were randomly divided into two groups: group A, 24 patients, underwent a second Tr-Ec with MMC and group B, 22 patients, also underwent a second Tr-Ec but without MMC. Postoperative complications included: shallow anterior chamber (duration > 1 week), group A 29.2%, group B 13.6%; chroidal effusion, group A 8.3%, group B 0%; cystic degeneration of conjunctiva, group A 16.6%, group B 4.5%; transient maculopathy, group A 12.5%, group B 0%. IOP control (< or = 20 mmHg after 18 months) was: group A 20 patients (83.3%) with mean 12.5 +/- 3.2 mmHg and group B 13 patients (63.6%) with mean 19.6 +/- 6.1 mmHg. In conclusion, the use of MMC in re-operation for primary open-angle glaucoma is associated with a higher rate of and more severe postoperative complications than Tr-Ec alone. However, it achieves significantly lower IOP in a larger number of patients.