Since the pioneer work of Wessely (1) in 1911 and of yon Szily and Arisawa (2) three years later, it has been well established that the cornea may be the site of a specific, antibody-mediated hypersensitivity reaction. This is generally manifested by a macroscopic ring of opacification in the cornea, appearing 13 or more days after the intralamellar inoculation of a soluble protein antigen. The intracorneal ring is composed of precipitated antigen-antibody complexes and inflammatory cells (3)(4)(5).In a previous study, the present authors demonstrated that if a sufficient quantity of antigen is introduced intracorneally in rabbits, one obtains a biphasic reaction in that cornea (6). The initial response is characterized by a sudden diffuse corneal clouding and a dilatation of the limbal vessels 3 to 5 days after the introduction of the antigen. It thus occurs during the early induction phase of the antibody-mediated reaction described above. At the time of the early corneal response, no humoral antibodies are demonstrable by either serological or histological techniques. In addition, the animals react to intradermal inoculation of small amounts of the specific sensitizing antigen with a delayed type of skin response and this sensitivity can be passively transferred to normal guinea pigs with the cells of pooled lymph nodes or buffy coats. Based on these observations, the earlier stage of the biphasic corneal reaction was considered a manifestation of delayed hypersensitivity.During the course of this biphasic hypersensitivity reaction, we were able to demonstrate a cellular infiltrate at the limbus of each experimental eye. Histologic study of the cellular elements composing this limbal infiltrate revealed a very definite evolutionary sequence. At the time of the delayed phase response, the inflammatory focus consisted predominantly of elements of the lymphocytic-mononudear series--the cells generally incriminated in delayed hypersensitivity. In contrast, during the later, antibody-mediated corneal ring response, the llmbal infiltrate consisted overwhelmingly of plasma cells. It is generally agreed that these cells are a major source of antibody at the cellular level and as such, are responsible for the latter type of immune phenomenon. In the interval between the two phases of corneal activity, the