The lymphocyte membrane was isolated from the calf thymocytes and the bovine intestinal lymphnode lymphocytes through a pretreatment with ZnCl(2) and Tween-20 combinig with a freeze-thawing procedure been followed by sucrose density gradient centrifugations. The recovery of lymphocyte membrane from the original lymphoid organ weight was 0.6 per cent (dry weight) and 0.9 per cent, as the lymphnode lymphocyte membrane (LM) and the thymic lymphocyte membrane (TM), respectively. Protein content in these preparations were 7.8 per cent and 2.3 per cent, in the LM and the TM, respectively. An amino acid content in the TM showed increased valine and leucine levels than the LM. Gel filtrations, using a Sepharose 4B column, of solubilized lymphocyte membranes revealed that the TM had higher protein content of larger molecular fractions than the LM. Disk electrophoresis also differentiated polypeptide bands between the LM and the TM. The morphological studies on these membrane preparations by a phase contrast microscope and an electron microscope demonstrated the purity of the membranes which was free from the contaminations of the microorganella. A rabbit was immunized with either one of lymphocyte membrane (TM of LM) with (intracutaneously) or without (intravenously) Freund's complete adjuvant. The circulating lymphocytes decreased more rapidly after the immunization of the TM than of the LM. The thymus, spleen, and lymphnode were atrophic macroscopically in the both groups. Histologically, however, more reduced lymphocytes in the tissue were observed in the group treated with the TM resulting a reduced cortical area with increased fatty degeneration in the thymus, been combined with a reduced lymphfollicular area in the spleen as same as the lymphnode than the group treated with the LM. Although a further elucidation is necessary, the lymphocyte membrane has shown specific antigenicity depending on the origin of the membrane upon the heterologous lymphoid organs.