Allogeneic dissociated spleen cells incorporated in Freund's complete adjuvant and injected s.c. induced a homograft response as radio-resistant as that produced by a skin graft. In two of three strains of mice studied, allogeneic dissociated spleen cells alone, when injected s.c., induced a homograft sensitivity only slightly less radioresistant than that induced by skin grafts. Anatomical separation of the injection sites of allogeneic dissociated cells and Freund's complete adjuvant produced a homograft response more radiosensitive than that induced by spleen cells alone.