Spleen and lymph node cells taken from strain 2 and strain 13 guinea pigs at the peak of their primary immune response to cutaneous syphilitic infection could transfer partial protection to symptomatic disease to normal syngeneic recipients challenged with the Nichols strain of Treponema pallidum. These recipients of immune cells had significantly fewer treponemes disseminating to the regional lymph nodes and developed fewer and less severe cutaneous lesions that resolved faster than those in guinea pigs that had been infused with normal lymphoid cells. Immune donor cells also had the capacity to transfer specific delayed-type hypersensitivity responses for T. pallidum antigens. Both T and B cells were effective in conferring anti-syphilis immunity which was associated with the almost immediate development and persistence of substantially elevated levels of circulating anti-treponemal antibody in the protected recipients. Our findings in this adoptive transfer system provide the first direct experimental evidence implicating both cellular and humoral components of the immune response as important effector mechanisms in host resistance to the pathogenic spirochete causing venereal syphilis.