The role of the measles virus (MV) receptor, human CD46, in the uptake of MV and antigen presentation by Major Histocompatibility Complex (MHC) class II molecules was investigated. Expression of CD46 in murine B cells resulted in cells highly efficient in capturing UV-inactivated MV particles and presenting both envelope hemagglutinin H and nucleoprotein N to specific T cell hybridomas. Although MV fuse with the plasma membrane of its target cells, presentation of both MV-H and -N was sensitive to inhibition by chloroquine but was not affected by a tripeptide which prevents virus-cell fusion. Whereas 50 μM of chloroquine was required to inhibit presentation of MV-H, purified H or soluble N, only a two-fold lower concentration was required to inhibit that of MV-N. This shows that some CD46-mediated captured MV particles are endocytosed, then disrupted and processed in an endosome/lysosome compartment.