It has been possible for the first time to demonstrate antibodies to homologous lens proteins in rabbits without the addition of adjuvant. By means of immunofluorescence and immunoperoxidase methods it has been possible not only to show for the first time that homologous lens antibodies cross-react with extraocular tissues but that the cross-reacting antigens are related to the cell mitochondria, microsomes, and the proteins associated with contractile organelles. The rabbits did not produce antibodies to gamma-crystallins even when the whole lens homogenate was injected with Freund's complete adjuvant. This suggests that gamma-crystallins are non-antigenic in homologous situations, and this may be related to both B- and T-cell tolerance. Alternatively, the failure of gamma-crystallins to induce antibody production may be due to intermolecular antigenic competition with other crystallins. The presence of mycobacteria in an adjuvant is essential for an antibody response to be detectable by agar diffusion techniques. The response to homologous lens antigens, both in magnitude as well as in duration, varied in different rabbits, which suggested to us that a central control mechanism involving the immune response (Ir) genes may plan an important role. Antibodies to homologous lens proteins as detected by immunofluorescence and immunoperoxidase methods were shown to be of the IgG class. This is the first time that the kinetics of the immune response to the same homologous lens antigen in saline with or without incomplete or complete adjuvant has been examined and their relative merits compared. Systemic homologous immunisation followed by discission of the lens led to a marked Arthus type reaction in and around the lens, but a typical granulomatous phakoallergic endophthalmitis was not produced. It seems likely that the rabbit is not suitable for the production of an experimental model of this condition.