Over the past year, considerable progress has been made in the understanding of the pathogenesis of a variety of infections found in the immunocompromised host. Some interesting organisms not previously described in this setting have been implicated as being causative of disease. Molecular methods for the detection of many organisms increase our ability to diagnose infection in these patients, and also make the accurate monitoring of infection during treatment possible. Curr Opin Infect Dis 11:437–440. 1998 Lippincott-Raven Publishers