This paper describes the development of computer software capable of simulating the structural response of steel-framed buildings in fire. The first part of the paper deals with the basic non-linear formulation of the program, which allows the three-dimensional response of steel members at elevated temperatures to be modelled. Recent extensions of the software, which allow the modelling of semi-rigid connections, lateral-torsional buckling, continuous floor slabs and strain reversal, are then discussed. Wherever possible, validation against test data or other independent computer software has been reported, together with illustrative examples. (C) 1998 Elsevier Science Ltd. All rights reserved.