The contrasting type of lesion produced in the first eye of non-immune and the second eye of the then immune rabbits using herpes simplex Type I virus is demonstrated. Cryosurgery may make the first eye worse but the second eye is healed. A large percentage of second eyes heal spontaneously, however, as circulating antibody titres are high. Artefacts may be mistaken for lesions in the immune eye but superficial viral growth has a characteristic plaque-like appearance. One hundred eyes with recurrent superficial, recurrent superficial stromal, disciform deep stomal, and metaherpes treated with cryosurgery and immunotherapy are discussed. An immediate cure was obtained in all cases. Seven cases recurred over the 10-year period studied, but these were all successfully re-treated. Corneal grafts were performed in twelve cases with failure in only one case.