Rabbits previously sensitized to rat cornea rejected within six to eight days the rat corneal buttons that had been placed in their vascularized corneas. Goat antirabbit lymphocyte serum (GARLS), administered systemically, significantly retarded or entirely prevented the development of the graft reaction. The subconjunctival administration of GARLS was irritating, and in the doses used it did not significantly alter the graft reaction. The white blood cell and lymphocyte counts dropped dramatically within several minutes after GARLS was injected systemically. Animals receiving normal goat serum systemically developed anaphylaxis and serum sickness after repeated injections, whereas animals receiving GARLS systemically did not show any side effects. Animals receiving GARLS systemically showed diminished numbers of lymphocytes in their thymus glands as well as enlarged and active spleens.