The fine structure of the pancreas of the South American three toed sloth, Bradypus tridactylus, is described. In exocrine cells two types of granules are found. The first variety of granules is circular, of about 0.9 micrometer mean diameter, and probably represents zymogen granules. The second type of granule is larger (up to 1.4 micrometer in diameter) and contains a granular electron-dense material which is separated from the limiting membrane by a wide space. Only one type of islet cell was found. It contains spherical membrane-bound granules of uniform size.