Soricine shrews are typified by the presence of reddish pigment in their tooth enamel. This coloration is caused by iron and is thought to make the enamel more resistant to wear. Ten specimens of Blarina brevicauda were examined for percentage iron concentration using a scanning electron microscope in conjunction with an energy-dispersive spectrometer. Substantial iron variation was found between individual molar cusps and between different tooth positions. Specifically, the cusps associated with crushing and grinding, as opposed to shearing, had more iron incorporated into their enamel. In addition, the enlarged m1 exhibits higher iron density than the more-posterior teeth. These results suggest that increased iron density is expressed on teeth, and parts of teeth, that are subject to greatest stresses and are most prone to fracture and excessive wear.