To better understand the mechanism(s) whereby antibody and complement and cytotoxic lymphocytes lyse infected cells, we studied the structure, interrelationship and turnover of measles virus polypeptides expressed on the cell's surface. Of the 6 major viral structural polypeptides, L, HA, P, NC, F, and M, found in purified virions or infected cells, only 2, the HA and F, resided on the surface of infected cells. The HA was present primarily in the form of a 160k dimer, and F was identified as a 64k polypeptide migrating distinct from other viral polypeptides. With reduction, the HA migrated as a 80k monomer, and F0, after cleavage, was found to be composed of a 42k nonglycosylated polypeptide, F1, and a 24k glycosylated protein, F2. The relationship between F0 and F1 and between the HA dimer and monomer was verified by tryptic peptide mapping. The turnover of HA and F from the cell's surface was 10 and 9 hr, respectively. However, in the presence of specific antibody after a marked loss of viral antigen from the surface, the turnover for HA and F was 15 and 12 hr, respectively. Despite being independent molecules, HA and F were closely linked, as they moved together (co-capped) over the plasma membrane when incubated with monospecific or monoclonal antibody. In contrast, neither HA nor F co-capped with the major histocompatibility antigens or with other host cell proteins, which indicates a separation between these host cell proteins and measles viral glycoproteins on the cell's surface.