The final report of an IAEA co-ordinated research programme involving nine organizations in eight Member States during the period 1977–1983. The irradiation response of seven steels typical of modern practice, in the form of plants, forgings and submerged arc welds supplied by worldwide suppliers, was determined under light water reactor pressure vessel irradiation conditions. Contents: Introduction; Scientific scope and programme goals; Standard part of phase 2 programme; Irradiation conditions; Experimental results; Discussion of results; Conclusions; Appendix A: List of participants in the programme; Appendix B: Materials specification and identification; Appendix C: Expressions used to define errors in linear regression analyses; Appendix D: Summary of experimental data; List of symbols and abbreviations.