Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Budding Cryptococcus neoformans with cell walls stained with calcofluor (blue) and a monoclonal antibody to capsular glucuronoxylomannan (green). The image was originally obtained at a magnification of ×400. Analysis of polysaccharide structure by mass spectrometry revealed that the major capsular polysaccharide is composed of different repeating units. Hence, the polysaccharide structure in this eukaryotic pathogen is fundamentally different than in bacteria, where polysaccharides are homopolymers composed of one type of repeating unit. The finding that individual molecules of glucuronoxylomannans can be heteropolymers raises the possibility of almost infinite structural diversity that would translate into antigenic variation. (See related article on page 1464.)