AIM:To study the changes of cell proliferation and apoptosisin rat jejunal epithelium at different ages.METHODS:Cell proliferation and apoptosis of the jejunalmucosal and glandulous epithelia from birth to postnatal12~(th) month were observed using immunocytochemistry(ICC),and TUNEL method.The height of villus,the thicknessof muscle layer and the number of goblet cells in jejunalmucosal and glandulous epithelia were measured byBeiHang analytic software and analyzed by STAT.RESULTS:(1) Proliferating cell nuclear antigen (PCNA) positivecells of jejunal glandulous recess were found and increased innumber from birth to the postnatal 3~(rd) month.The number ofPCNA positive cells peaked in the postnatal 3~(rd) month,anddecreased from then on.(2) The number of apoptotic cellsalso peaked in the postnatal 3~(rd) month,showing a similar trendto that of the PCNA positive cells.(3) The height of jejunalvillus increased after birth,peaked in the postnatal 3~(rd) monthand decreased from then on.The jejunal muscle layer becamethicker in the postnatal 3~(rd) week and the postnatal 12~(th) month.The number of goblet cells of the jejunal mucosal andglandulous epithelia had a linear correlation with age.CONCLUSION:(1) PCNA positive cells are distributed inthe jejunal glandulous recess.(2) Apoptotic cell numberpeaks in the postnatal 3~(rd) month,indicating that cellproliferation and apoptosis are developed with the formationof digestive metabolism as rat grows to maturity.(3) Thethickness of jejunal muscle layer increases to a maximum inthe postnatal 3~(rd) week,which may be related to the changein diet from milk to solid food.(4) The number of gobletcells increases rapidly in the postnatal 3~(rd) week,probablydue to ingestion of solid food. AIM: To study the changes of cell proliferation and apoptosisin rat jejunal epithelium at different ages.METHODS: Cell proliferation and apoptosis of the jejunal mucosal and glandulous epithelia from birth to postnatal 12 ~ (th) month were observed using immunocytochemistry (ICC), and TUNEL method The height of villus, the thickness of muscle layer and the number of goblet cells in jejunal mucosal and glandulous epithelia were measured byBeiHang analytic software and analyzed by STAT.RESULTS: (1) Proliferating cell nuclear antigen (PCNA) positive cells of jejunal glandulous recess were found and the increased innumber from birth to the postnatal 3 ~ (rd) month.The number of PCNA positive cells peaked in the postnatal 3 ~ (rd) month, anddecreased from then on. (2) The number of apoptotic cells rose peaked in the postnatal 3 ~ (rd) month, showing a similar trend to that of the PCNA positive cells. (3) The height of jejunalvillus increased after birth, peaked in the postnatal 3 ~ (rd) monthand decreased from then on. jejunal muscle layer became trigger in the postnatal 3 ~ (rd) week and the postnatal 12 ~ (th) month. The number of goblet cells of the jejunal mucosal and gllandular epithelia had a linear correlation with age. CONCLUSION: (1) PCNA positive cells are distributed inthe jejunal glandulous recess. (2) Apoptotic cell numberpeaks in the postnatal 3 ~ (rd) month, indicating that cellproliferation and apoptosis are developed with the formation of digestive metabolism as rat grows to maturity. (3) The thickness of jejunal muscle layer increases to (4) The number of gobletcells increases rapidly in the postnatal 3 ~ (rd) week, probablydue to ingestion of solid food .