Summary In hookworm disease parasitic attachment of the adult worms to the intestinal wall appears to be associated with intense eosinophilic reactions locally in the mucosa and even in the submucosa. Concentrated eosinophilic assemblage in the submucosa may indicate deep penetration by the worm. Hemosiderin pigments seen in the biopsy material could represent either hemorrhagic residue or reabsorption of iron lost into the intestine.