Pooled rabbit kidneys were extracted to yield an opalescent highly-proteinaceous material. This antigenic preparation was injected five days a week either intravenously or intraperitoneally into normal rabbits. After four weeks of this regimen, the animals were skin grafted from normal donors. Survival times of the graft were observed to be neither accelerated or retarded compared to a control series. The only consistent hematologic finding was an increased platelet count shortly after starting the injections. The second part of these experiments was directed towards growing dog spleen cells in tissue culture, and retrieving transplantation antigens from the media. The media in which cultured spleen cells grew did contain material which when injected into dogs immunized them against future kidney homografts from the donor of the cultured spleen cells. An attempt to show that RNA administration resulted in prolongation of skin homograft survival in rabbits failed to demonstrate an effect of RNA on skin homograft survival when the donor RNA was infused into recipient rabbits.