Small intestinal mucosal samples from man, pig and dog, were subjected to sequential or correlative silver impregnation techniques, applied to immunocytochemical preparations and at the ultrastructural level. The cell reacting with anti-GIP sera was identified as the ultrastructurally classified K cell and we propose that the term GIP cell be used in place of the latter. This cell can thus be recognized by its strong reactivity with the Sevier-Munger staining procedure, provided that the equally strongly reacting EC cell is excluded by virtue of its argentaffinity with the Masson technique.