We have studied the developmental and regional expression of mRNAs encoding sodium-dependent and facilitative glucose transporter proteins in human fetal and adult small intestine. The abundance of mRNAs encoding the Na(+)-glucose cotransporter isoform SGLT1 and the facilitative glucose transporter isoforms GLUT2 and GLUT5 is developmentally modulated with highest levels in adult small intestine. By contrast, the levels of GLUT1 mRNA are higher in fetal than adult small intestine. Immunohistochemical analysis of adult small intestine localized GLUT5 to the luminal surface of mature enterocytes, a finding confirmed by Western blot analysis of purified human jejunal brush-border membranes. By contrast, in the fetal small intestine, GLUT5 was localized along the intercellular junctions of the developing villus, indicating that both its expression and localization are developmentally regulated. The localization of GLUT5 to the luminal surface of mature absorptive epithelial cells implies that this protein participates in the uptake of dietary sugars.