THE lamina propria has its own lymphatic organ with immuno-competent cells. The secretions of the mucous membranes contain, besides IgG and IgM, predominantly immunoglobulin IgA1, which seems to be produced in the lymphatic part of the lamina propria and secreted into the intestinal lumen2. Here the epithelial cells may play a special role by producing the so-called T piece that links 7S IgA to an 11S unit3.