We have investigated the structure and interaction of the measles virus (MV) glycoproteins expressed at the cell membrane. Cross-linking studies with a variety of chemicals stabilized dimeric forms of the haemagglutinin (HA) or fusion (F) proteins, although by sucrose density gradient analysis, oligomers corresponding to tetramers and larger were observed for both proteins. In cells in which both HA and F were expressed at the surface, their close association was shown by cross-linking and co-immunoprecipitation.