Albino mice were immunized with a suspension of sheep erythrocytes. On the fifth day following treatment the animals were killed and B lymphocytes were isolated from their spleen tissue. Both the complement-fixation test and the immunofluorescence method were employed to specify the number of immunoglobulin receptors on the membrane surface, and disk electrophoresis was used to separate the protein fractions of the solubilizates from their membranes. Normal lymphocytes, obtained from unimmunized animals, were used as controls. It was established that: 1. The immunoglobulin receptors gradually decreased in number is the stimulated lymphocytes. On the fifth day of immunization their amount was 6.6 times lower than that in the normal lymphocytes. 2. The receptors in the normal lymphocytes proved diffusely scattered on the cell surface, while those in the stimulated lymphocytes were concentrated into clusters at one of the cell poles. The biologic nature of the observed changes is briefly discussed. It is concluded that the mature antibody-producing cell is not dependent on the antigen.