Irradiated 304 and 316 stainless steel samples were investigated. The steels were neutron irradiated to 1.5 and 7.5 dpa at 550 K. Similar types of steels were irradiated at 550 K with 590 MeV protons in the PIREX facility at PSI, Switzerland. The doses reached in this case were 0.15 and 0.3 dpa. The stress-strain relationships at different temperatures were measured. The irradiation and deformation microstructures were investigated using transmission electron microscopy (TEM). Two modes of deformation were found, twinning and channelling, depending on the testing temperature. These results are discussed in terms of deformation mechanisms at different temperatures correlated with radiation hardening. Finally, possible correlations between deformation modes and previous irradiation assisted stress corrosion cracking (IASCC) studies are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.