The authors have evolved an empirical method for characterising the resistance to ductile fracture using two parameters Γ f and η f that can be determined from tensile test data of smooth cylindrical specimens. This method stipulates that the post-necking regime during tensile deformation is dominated by microvoid growth and coalescence processes, and therefore the energy absorbed in this regime can be used to estimate the resistance of the necked region to ductile fracture. The test procedure employed is simple and does not require gauge-length extensometry—a distinct advantage at non-ambient temperatures. The test is carried out in a screw-driven machine at a constant cross-head speed, with on-line computerised acquisition of load-time data; it is also necessary to have a prior precise calibration for the (non-linear) elastic deformation of the load train. The method of computing Γ f and η f from tensile test data is described, and its engineering application demonstrated by characterising the effect of ageing for three dissimilar metal welds, namely Alloy 800/2.25Cr-1Mo steel and Alloy 800/9Cr-1Mo steel (both from tests at 300 K) and type 316LN stainless steel/Alloy 800 (from tests at 773 K); from the results for the Alloy 800/Cr-Mo steel weldments the optimum post-weld heat-treatment temperatures could also be derived.