The structure, cellular composition and organization of the small intestinal epithelium of adult Xenopus laevis are described. The mucosa is thrown into a system of longitudinal folds and is composed mainly of columnar cells and goblet cells. Leucocytes comprise about 28% of the mucosal cells. The degree of structural specialization of columnar cells varies according to their position in the folds. Cells at the crest of the folds display the greastest degree of specialization, evidenced by the degree of development of their inter- and intracellular membrane systems. Cells in the trough regions between the folds are much less specialized. These cell types are structurally analogous to mammalian villous and crypt cells respectively, although they are not segregated to the same degree.