[en] In order to investigate the effects of crystallographic orientation on deformation and crack initiation in iodine-induced SCC of zirconium alloys, uniaxial tensile tests of zirconium and Zircaloy-2 plates were conducted in an iodine atmosphere. The crystallographic orientation of individual grains was determined by an etch-pit technique prior to testing. After testing, the etch-pit technique showed that prismatic slip was predominant in the plastic deformation and that cleavage cracks extended along basal planes. The plastic deformation of individual grains was significantly influenced by their crystallographic orientations, which varied from one grain to another. Accordingly, in homogeneous plastic deformation occurred between grains. The crack initiation took place preferentially at grain boundaries where differences of crystallographic orientations were large between adjacent grains. This indicated that crack initiations was caused by stress concentration due to strain incompatibility at those grain boundaries. (orig.)