A finite element formulation is presented for the large deflexion elasto-plastic analysis of thin mild steel plates subject to buckling loads. The method can be used to trace the behaviour of imperfect steel panels over the full load range, including the unloading stage following collapse. A series of simply supported plates under uniaxial compression has been analysed to study different in-plane boundary conditions, levels of geometric imperfection and residual stress. An approximate method is proposed for handling residual stresses and load-shortening curves are derived. These load-shortening relationships are used in a 'column' analysis to predict the behaviour of wide eccentrically stiffened plating subject to uniaxial compression. The computed collapse loads for both the individual plates and the stiffened plating are compared with experimental results. (A) /TRRL/