Jejunal secretion of albumin, immunoglobulins and secretory component was studied using the segmental perfusion technique with an occluding balloon, in two patients with common variable hypogammaglobulinemia and one patient with selective immunoglobulin A deficiency. Results were compared with those of twenty-two controls previously studied under the same conditions. In all three cases, jejunal secretion rate of immunoglobulin A was nil and secretion rates of albumin and immunoglobulin G were increased as compared to controls. Jejunal secretion rate of immunoglobulin M was increased in the patient with selective immunoglobulin A deficiency, normal in one case of common variable hypogammaglobulinemia and almost nil in the other case. Secretory component was secreted in the jejunal lumen mostly or exclusively under a free form depending on partial or total absence of immunoglobulin A and M. This study allowed to confirm in vivo that secretion of secretory component is independent of the presence of immunoglobulins. Intestinal perfusion might be a useful tool in the investigation of immunological diseases of the intestinal tract.