The purpose of this paper is to describe an interactive computer graphics approach to the analysis and design of structures exhibiting nonlinear structural behavior. A general procedure for the nonlinear analysis of planar frame structures, which accounts for member yielding, is described. In addition, the graphics programs required to input an arbitrary planar structure, monitor the analytical procedure, and aid in evaluating the results of the incremental analysis are presented. A procedure for generating a color image of the deflected structure, where the color indicates the proximity to yield, is also presented. This interactive approach to a powerful analysis procedure, aided by graphic interpretation of input and analysis results, provides a practical desïgn tool.