When exposed to high levels of human immunodeficiency virus (HIV), the cells lining the mouth can develop a low-level infection, a finding that increases our understanding of the risks of oral transmission of the disease. Researchers from Charles R. Drew University and the University of California, Los Angeles, report their findings in the March 2003 issue of the Journal of Virology. “The majority of HIV type 1 infections occur via mucosal contact, and there are several reports indicating that the oral mucosa may be one route of exposure,” say the researchers. “It is difficult to confirm that oral mucosa is a major transmission portal because of the correlation between oral-genital contact and other transmission risk behaviors.”