The potentiometer circuit designed for measuring minute variations in small resistances developed by P. W. Bridgman has been used to measure the effect of tension, applied in a direction parallel to that of the current, on the resistance of iron single crystals (elastoresistance). Correction for strain permitted the calculation of the more informative physical characteristic, the elastoresistivity. In order to obtain at least an indication of the expected anisotropy of elastoresistivity, two single crystals of different orientations were investigated. Deformation temperatures of +30° and −78°C were used to observe the effect of temperature on the (relative) elastoresistivity. The increase in &Dgr;&rgr;/&rgr; with decreasing temperature was larger than anticipated. The elastoresistivity and elastoresistance showed considerable anisotropy.