An extensive investigation of the lymphatic drainage from the rat testis was carried out in an effort to detect any characteristics which might be important in the immunological privilege the testis extends to allografts. Three different methods revealed a consistent and very efficient lymphatic drainage involving primarily the iliac and renal lymph nodes and to a lesser extent the external lumbar, para-aortic, and posterior gastric nodes. Within minutes, dye or labeled cells injected into the testis could be found within regional nodes. Node hypertrophy was induced by injecting the testes of F1 hybrids with parental strain lymphoid cells (a regional graft-versus-host reaction). Besides indicating that efficient filtration occurs in these nodes, this also established that they are a hospitable environment for cellular immune reactions. Similarly, the capacity of allogeneic cells injected into the testis to induce production of humoral alloantibodies by recipients confirms that exposure to antigens via this route does not in itself suppress immune responsiveness.