For one to understand better the immunological mechanism in the colonic mucosae of inflammatory bowel disease, 19 children with ulcerative colitis and 12 children with Crohn's disease were studied. The inflammatory cells identified by the immunoperoxidase technique and specific markers for total T lymphocytes (CD3), helper T lymphocytes (CD4) and B lymphocytes (CD20) in differents evolutionary periods of the disease were analysed. PI (before treatment), PII (until two years of treatment) and PIII (with more than two years of treatment). In general, all marker studied in this research, presented higher averages if comparing to the control group with different degrees of significance in the different studied periods. The marker CD3, of the total T lymphocyte, increased in the epithelial (superficial and glandular) and in the lamina propria of the involved mucosae in relation to the controlled ones, was diffusely distributed over the mucosae, concentrating itself around the microgranulomas and the nodules lymphoids. In Crohn's disease, PI, its average differed significantly from the controlled ones. Similar behave was seen in the marker CD20 of the lymphocytes in the involved mucosae, whole averages were superior in relation to the controlled ones; thought, only in the PI of the Crohn's disease this difference had been significant. The immunochromatic cells CD3 distributed themselves diffusely over the involved mucosae, concentrating themselves in the interior of the lymphoides nodules and in the injured areas, near the macrophages. The marker CD4, of helper T lymphocyte also presented in the involved mucosae high averages in relation to the controlled mucosae, but without estatistic significance. The CD4 cells distributed themselves diffusely over the whole thickness of the involved mucosae, concentrating themselves around the lymphoids nodules and microgranulomas. These results confirm the participation of these elements in the pathogenesis of inflammatory bowel disease, but did not permit the establishment of any discriminatory criteria between ulcerative colitis and Crohn's disease. The results of positive correlation between the increased of CD4 and CD20 in ulcerative colitis and CD3 and CD20 in Crohn's disease show clearly the immunoregulation action of the CD4+ cells over clonal expansion and the differenciation of the B lymphocytes from plasmocytes and the IgG syntese.