SUMMARYRectilinear dislocation loops are observed to grow in thin foils of α‐iron during 1 MeV electron irradiation at 550°C in the beam of a high voltage electron microscope. A diffraction analysis indicates that the loops have sides parallel todirections and are pure edge withaBurgers vector. Only interstitial type loops have been identified. The geometry of the loops can be accounted for by an established model of loop nucleat