The effectiveness of immunizing mice with protease toxoid (PT) or elastase toxoid (ET) on the corneal ulcerization due to either protease or elastase were investigated. Mice immunized with PT or ET were protected from corneal ulcers experimentally induced by the homologous enzyme, either protease or elastase. Rabbit anti-PT and anti-ET, prevented corneal ulcers by the homologous enzyme. The therapeutic effects of vaccination with a single or mixed vaccine consisting of PT, ET and/or the common antigen (OEP) of P. aeruginosa, were examined on corneal ulcers in mice produced by live cultures of the bacteria. Administration of a single or combined rabbit immune sera against PT, ET and OEP was also conducted. Vaccination with the 3 component-mixed vaccine or administration with rabbit immune sera combined with anti-PT and anti-ET sera in addition to anti-OEP serum were the most effective in preventing corneal ulceration and in treating corneal ulcers in mice.