Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): Aspergillus fumigatus is a mold that causes invasive disease in immunocompromised hosts. Mortality rates associated with A. fumigatus infection are very high. In these lung sections obtained from a neutropenic mouse following aerosol infection, the organism is shown to invade the lung parenchyma from the bronchus. Angioinvasion and tissue necrosis (seen to the right of the blood vessel) are important aspects of the pathogenesis of aspergillosis. Fungi may be difficult to see in tissue after routine staining (hematoxylin and eosin) (left panel). However, more extensive growth and vascular invasion can be revealed by using special stains (e.g., Gomori methenamine silver, shown here) (right panel). (See related article on page 114.)