A modified model of conjunctival immediate hypersensitivity in the rat is described. The advantages of this model over previously reported rat models are that it does not require invasive challenges, pre-treatment with mucolytic agents to enhance antigen penetration, or the use of haptens, and is therefore more representative of the mode of allergen challenge seen in human hay fever conjunctivitis. This model has been shown to have both early and late-phase cellular responses but only early phase clinical signs. During the early phase of the response the tarsal region accommodates a massive neutrophil infiltration and the fornix-bulbar region participates to a greater extent during the late-phase reaction, with a significant eosinophil infiltration. The development of this model has allowed us to gain a clearer insight into the mechanisms involved during conjunctival immediate hypersensitivity in the rat; and the simplicity of this model makes it attractive to use in the evaluation of new drug therapies prior to their introduction into human clinical trials.