The significance of the ultimate failure load of a structure is widely recognized, yet its determination has been a considerable task. Various propositions have been put forward since the formulation of the well-known plastic theory. These have been either of empirical nature such as the Merchant-Rankine formula or laborious such as the method of following the sequence of hinge formation. In this paper the main propositions are discussed briefly. A method is then presented to evaluate the failure loads of plane frames without following the sequence of plastic hinge formation. Instead the method utilizes the elastic as well as plastic load-deformation characteristics of frames, including the second-order effects involved in both. The theoretical validity of the proposed method is studied and illustrative examples are given. Comparisons are then made with experimental observations on frames loaded proportionally up to collapse. A summary of a computer approach is presented, but throughout the paper attention is also paid to manual procedures.