The inhibitor N-[2R-2-(hydroxamidocarbonymethyl)-4-methylpentanoyl)]-L- tryptophan methylamide specifically blocks several matrix metalloproteases, enzymes which are thought to be involved in angiogenesis. An extract of Walker 256 carcinoma in Hydron pellets implanted in the corneas of Sprague-Dawley rats was used to stimulate angiogenesis from the vessels of the limbus. Angiogenesis was graded visually as the distance penetrated into the cornea and the number of vessels generated. The vessel area was also measured by image analysis using Image 1 software. Continuous i.v. administration of N-[2-(hydroxamidocarbonymethyl)-4-methylpentanoyl)]- L-tryptophan methylamide at 32 mg/kg/day (n = 17) via syringe pump reduced vessel number [25.06 +/- 5.9 (SEM) compared to 65.33 +/- 9.0] and vessel area (26.14 +/- 3.2 mm2 compared with 40.96 +/- 4.6 mm2), but not distance penetrated, compared to vehicle-treated control eyes after 6 days. These results confirm the suspected role for matrix metalloproteases in angiogenesis and suggest that inhibitors of these enzymes may be angiostatic agents.