We previously identified Candida albicans Not5p as an immunogenic protein expressed during oropharyngeal candidiasis (OPC). In this study, we demonstrate that C. albicans NOT5 reverses the growth defects of a Saccharomyces cerevisiae not5 mutant strain at 37 degrees C, suggesting that the genes share at least some functional equivalence. We implicate C. albicans NOT5 in the pathogenesis of disseminated candidiasis (DC) induced by intravenous infection among neutropenic and nonimmunosuppressed mice, as well as in that of OPC in mice immunosuppressed with corticosteroids. We find no role in virulence, however, among neutropenic and corticosteroid-suppressed mice with DC resulting from gastrointestinal translocation, nor do we implicate the gene in vulvovaginal candidiasis among mice in pseudoestrus. These findings suggest that the role of NOT5 in virulence depends on the specific in vivo environment and is influenced by diverse factors such as tissue site, portal of entry, and the status of host defenses. NOT5 is necessary for normal adherence to colonic and cervical epithelial cells in vitro, demonstrating that such assays cannot fully replicate disease processes in vivo. Lastly, antibody responses against Not5p do not differ in the sera of patients with OPC, patients with DC, and healthy controls, suggesting that the protein is associated with both commensalism and the pathogenesis of disease.