The authors have evolved an empirical method for characterizing resistance to ductile fracture using two parameters Γf andηf 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 tests are carried out in a screw-driven machine at a constant crosshead speed, with online computerized acquisition of load-time data; it is also necessary to have a prior precise calibration for the (nonlinear) elastic deformation of the load train. The method of computing Γf and ηf, from tensile data is described, and its engineering application demonstrated by characterizing the effect of ageing of two dissimilar metal welds, namely Alloy 800/2.25Cr-lMo steel and Alloy 800/9Cr-1Mo steel. From these results, it has been established that this procedure of estimating the ductile fracture toughness from tensile tests can be used as a simple, practical method for optimisation of post-weld heat treatment of weld joints.