Immunofluorescence shows that the oxyntic mucosa of a dog depancreatized for 5 years and having a poorly-controlled diabetes has more glucagon-and somatostatin-containing cells than the mucosa of a control dog. At the ultrastructural level, 4 endocrine cell types are identified: A-, A-like, D-and enterochromaffin-like (ECL) cells, with increased numbers of A-, A-like and D-cells in gastric glands of the depancreatized dog, together with a higher concentration of immunoreactive glucagon in the gastric mucosa. The increase in A-, A-like and D-cells is compatible with: a) a change induced by the diabetic state itself; b) a hyperplasia secondary to the loss of corresponding pancreatic cells. At any rate, the fact that A-, A-like and D-cells increase parallely may indicate that these three cell types are functionally related one with another.