Normal human peripheral blood lymphocytes were studied with fluorescent anti immunoglobulin antibodies and shown to have a patchy distribution of immunoglobulin on their surfaces that does not form a cap after complexing with antibody. Use of freeze etch electron microscopy confirmed the distribution of immunoglobulin in isolated patches on the membrane. Evidence is presented that this distribution may explain the absence of capping of these human cells as compared with mouse B lymphocytes. Studies of the metabolism of antibody bound to the cell surface revealed rapid shedding of complexes from the cell and also rapid endocytosis with subsequent degradation of the antibody. Several attempts to alter this distribution of immunoglobulin on the surface were unsuccessful. Possible mechanisms by which cell surface elements may be organized are discussed, as well as the significance of the results in terms of the immune response and the classification of certain lymphoproliferative diseases.