Secreted aspartyl proteinases are putative virulence factors in Candida infections. Candida albicans possesses at least nine members of a SAP gene family, all of which have been sequenced. Although the expression of the SAP genes has been extensively characterized under laboratory growth conditions, no studies have analyzed in detail the in vivo expression of these proteinases in human oral colonization and infection. We have developed a reliable and sensitive procedure to detect C. albicans mRNA from whole saliva of patients with oral C. albicans infection and those with asymptomatic Candida carriage. The reverse transcription-PCR protocol was used to determine which of the SAP1 to SAP7 genes are expressed by C. albicans during colonization and infection of the oral cavity. SAP2 and the SAP4 to SAP6 subfamily were the predominant proteinase genes expressed in the oral cavities of both Candida carriers and patients with oral candidiasis; SAP4, SAP5, or SAP6 mRNA was detected in all subjects. SAP1 and SAP3 transcripts were observed only in patients with oral candidiasis. SAP7 mRNA expression, which has never been demonstrated under laboratory conditions, was detected in several of the patient samples. All seven SAP genes were simultaneously expressed in some patients with oral candidiasis. This is the first detailed study showing that the SAP gene family is expressed by C. albicans during colonization and infection in humans and that C. albicans infection is associated with the differential expression of individual SAP genes which may be involved in the pathogenesis of oral candidiasis.