Iron pigments of hemochromatosis of man and of enterosiderosis (pseudomelanosis) of the guinea pig intestine are desiderized by extraction with aqueous solutions of sodium dithionite (5%, 15 min) and of [beta]-mercaptoethanol (10%, 24 hours). Pretreatment of 5 [mu] sections with 50 or 100 mM ammonium sulfide (24 hours) renders these pigments resistant to extraction either by dithionite or by [beta]-mercaptoethanol. The dithionite reduces the iron largely to the ferrous state, the [beta]-mercaptoethanol is less effective and part of the demonstrable iron remains ferric. Solutions of 1% potassium ferro and ferricyanide, both in 0.125 N HC1, are used as demonstration agents for iron. It is concluded that since cecal iron of the guinea pig does not resist extraction by Na2S2O4 or HSC2H4OH until deliberately converted to sulfide, that it does not exist as sulfide in freshly fixed cecum, and that the reported occurrences of iron sulfides in human intestinal tissue is a postmortem phenomenon.