Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Detection of the hemagglutinin (H) protein by indirect immunofluorescence in Vero cells infected with a rodent brain-adapted strain of measles virus (CAM/RB). Syncytia of more than 50 cells were generated upon infection. A primary mouse monoclonal antibody was used to detect the H protein in syncytia, and a fluorescein isothiocyanate-conjugated secondary antibody was used for indirect immunofluorescence (green). Nuclei were counterstained with propidium iodide (red). Micrographs represent 8- to 10-µm-deep composite optical sections. Magnification, ×160. (See related article on page 7612.)