Summary: In the experiments reported here, dogs have been shown to be capable of displaying delayed cutaneous reactions indicative of homograft immunity as the result of the inoculation of homologous lymphoid cells. Direct reactions (in sensitized recipients), transfer reactions (of specifically competent lymphocytes to normal recipients), and normal lymphocyte transfer reactions develop in a fashion essentially similar to that described in guinea-pigs, hamsters and man. Attempts to produce skin lesions in irradiated hamsters using dog lymphoid cell mixtures were unsuccessful.