AbstractThe electron microscopic localization of insulin, glucagon, somatostatin, and pancreatic polypeptide (PP) in the pancreas of the iguanid lizard,Anolis carolinensiswas studied by the unlabeled antibody peroxidase‐antiperoxidase immunocytochemical technique. Insulin, glucagon, and somatostatin were localized absolutely to those cells previously identified on the basis of the characteristics of their secretory granules as being β cells, α cell, and D cells, respectively. The secretory granule cores of the PP‐containing cells appeared to be ellipsoidal with a semi‐major axis of 450 nm and a semi‐minor axis of 365 nm. This previously unidentified cell type is named the F cell, in keeping with the localization of PP to the original F cell of the canine pancreas. Without immunocytochemical staining, the qualitative ultrastructural characteristics of the F cell secretory granules were inadequate to permit certain identification of the F cell, especially with regard to t