The fusion protein of respiratory syncytial virus (RSV-F) is responsible for fusion of virion with host cells and infection of neighbouring cells through the formation of syncytia. A three-dimensional model structure of RSV-F was derived by homology modelling from the structure of the equivalent protein in Newcastle disease virus (NDV). Despite very low sequence homology between the two structures, most features of the model appear to have high credibility, although a few small regions in RSV-F whose secondary structure is predicted to be different to that in NDV are likely to be poorly modelled. The organization of individual residues identified in escape mutants against monoclonal antibodies correlates well with known antigenic sites. The location of residues involved in point mutations in several drug-resistant variants is also examined.