The microstructure and tensile behavior of pure single crystalline Ni irradiated to low doses at room temperature with 590 MeV protons are investigated. Tensile tests performed at room temperature show radiation induced hardening, which increases with increasing dose. The microstructure of irradiation induced defects observed under transmission electron microscopy consists of about 50% stacking fault tetrahedra, 30-40% dislocation loops and 10% of unidentified features. In addition, the irradiated and deformed specimen microstructure exhibits, at the beginning of deformation, shear bands as straight channels that are free of defects. The macroscopic results of the localized deformation have been observed during tensile test. The surface topography evolution is discussed in terms of localized shear and crystal rotation, which relates to the formation of deformation cells. (C) 2003 Elsevier B.V. All rights reserved.