Sera, intestinal secretions and intestinal biopsies were collected from twelve biopsy-proved lepromatous leprosy patients with the help of a capsule invented by Roy Choudhury. Sera from another twenty-five proved lepromatous cases were also included. Sera and intestinal aspirates from twenty-five normal subjects and twenty patients with intestinal tuberculosis were also taken as controls. Acid-fast organisms, morphologically resembling Mycobacterium leprae, were detected in the intestinal aspirates of only two leprosy patients. Immunoglobulin levels in their sera and elevation secretions were estimated by the single radial immunodiffusion technique. Significant elevation of serum IgG, IgA and IgM, selective IgA deficiency in intestinal aspirates and flattening of intestinal villi along with mononuclear cell infiltration were conspicuous observations in the leprosy group. On the other hand, the patients with intestinal tuberculosis showed elevation of the IgG level in serum as well as in the intestinal secretions. It was postulated that persistent challenge by M. leprae or its antigens to the IgA immunocytes of the intestinal epithelium might have induced tolerance leading to IgA deficiency and subsequent subtotal atrophy of the intestinal villi in the patients with lepromatous leprosy.