The functional activity of the epithelial cells of the intestinal folds of Xenopus was analysed histochemically. There is a gradient of increasing absorptive, digestive and secretory activity from the trough regions to the crests of the longitudinal folds. The differences in functional activity correspond to differences in structural complexity, and confirm the existence of a more specialized population of cells at the fold crests and a less specialized population at the fold troughs, analogous to mammalian villous and crypt cells respectively.