We describe a patient transfused with 200 ml of donor fresh whole blood three times at 2-week intervals. Three weeks after the last transfusion, transplantation and splenectomy were done at the same time. Splenic cells from this DST pretreated patient were fused with murine myeloma cells (X63-Ag8, 653). With DST pretreatment, various clones were developed in vivo, and finally 69 human immunoglobulin-secreting clones were obtained. Modulation of the alloantigen-specific MLR by supernatants from 69 clones showed various degrees of suppression or augmentation. The hybridoma clone 7 and clone 2, which had been secreting IgG antibody for more than 6 months, showed some degree of suppression in the alloantigen-specific MLR (mean suppression = 63%, 46% respectively). According to the result of MLR, clone 7 antibody was directed against recipient lymphocytes and clone 2 antibody was against donor lymphocytes. Immunoprecipitation was carried out by clone 7-IgG and clone 2-IgG. Clone 7-IgG specifically precipitated 1 molecule from the recipient lymphocyte with a molecular weight of 120 KD, similar to the molecular weight range reported for T cell receptors. Clone 2-IgG precipitated a 20 KD molecule from the donor lymphocyte. The data suggest that DST induces antibodies directed against the blood donor alloantigen-specific receptors on the recipient's T lymphocytes--and, at the same time, induces antibodies against donor lymphocyte antigens. These antibodies may be essential to prolongation of kidney allograft survival following DST.