A method is described for observing the austenite‐martensite transformation in steel by measuring electrical resistance. Small wire samples are heated and cooled either in vacuum or in air while temperature and resistance are automatically recorded. Temperature throughout the sample is uniform enough to permit a determination of resistance as a function of temperature. It is shown that from these data a complete record of transformation during cooling can be computed. Such transformation data have been obtained on three steels of widely different compositions, representing the types of steel in which transformation is most difficult to observe.