Biopsies of the jejunum from 61 children, 6 months-4 years of age, including 35 with allergy to corn protein, 18 with celiac disease and 8 children without stomach and intestine pathology were studied. Biopsies were fixed in 10% formalin or in Carnois fixative, the sections were stained with hematoxylin and eosin, 0.5% toluidine blue (pH 0.5), and immunoperoxidase method was used for revealing IgA. The structure of the mucosa was not changed in the allergic patients, the content of the granulated and ungranulated labrocytes was increased, their number being decreased in the elimination diet. The number of plasma cells was diminished, and in only few of them IgA was found in children with severe alimentary malabsorption. A selective deficiency of IgA was diagnosed which determines the therapy of such children. Hyperregenerative atrophy of the mucous membrane and predominance of degranulated cells over undergranulated were noted in celiac disease.