A three-dimensional non-linear procedure is presented for modelling partial shear connection in composite steel-framed buildings in fire. The model has been incorporated within the computer program VULCAN which has been developed to model such structures. The accuracy and reliability of the model are demonstrated by analyses of four previously tested simplysupported composite beams, of which two were tested at ambient temperature, and a major full-scale fire test conducted in the Cardington composite test frame. The model is clearly capable of predicting the response of composite members and structures in fire with acceptable accuracy, although data is needed on the degradation of shear stud connectors at elevated temperatures. It is shown that, in statically determinate components, the local failure of shear studs can very rapidly alter the behaviour at the failure temperature, although whether this is important depends on the loading level. The inclusion of partial interaction is shown to make a small, but potentially significant, amendment to the analytical results in the high temperature range for the three-dimensional full-scale fire test.