Gastrointestinal (GI) tracts from four anuran and four urodele species were examined macroscopically and histologically from the esophagus to the cloaca. Anatomic observations were facilitated by treating the GI tracts with acetic acid, a procedure which removes gut epithelium and exposes underlying structures. Histologic analysis involved routine as well as specific histochemical techniques. Detailed observations reveal that anuran amphibians possess nodular, well-organized gut-associated lymphoid tissue (GALT) throughout their GI tracts. In striking contrast, no such patterns of lymphoid tissue have been noted in the Urodela. Similar techniques have revealed the location of lymphoid tissues in the urogenital system (e.g., cloaca and bladder) of advanced anurans. These nodules appear to be lacking in the primitive anuran Xenopus and in all the urodele species we examined. Preliminary observations have confirmed GALT and urogenital-associated lymphoid tissues in the snapping turtle.