• Interleukin 1 incorporated into Elvax-40 (ethylene-vinyl-acetate copolymer consisting of 40% vinyl-acetate by weight) induces a rapid and strong angiogenic stimulus when implanted in rabbit corneas at a distance of 2.5 mm from the limbus. A constant and reproducible neovascular stimulus was observed with 5 ng per implant of recombinant human interleukin 1 alpha or 100 ng per implant of recombinant human interleukin 1 beta. At these concentrations, neither tumor necrosis factor nor interleukin 2 induced any neovascular stimulus. These data are interpreted as an indication for the possible role of interleukin 1 in angiogenesis of ocular (and other) tissues. As interleukin 1 is produced by various cells, it is hypothesized that this molecule may be the "unitarian angiogenic factor."