We describe a rapid and reproducible PCR assay for quantitation of the Candida albicans ribosomal DNA (rDNA) in clinical blood samples based on the TaqMan principle (Applied Biosystems), in which a signal is generated by cleavage of a template-specific probe during amplification. We used two fluorogenic probes based on universal, fungus-specific primers, one for the detection of C. albicans species DNA and one for the detection of all Candida genus DNA. C. albicans blastoconidia mixed with whole blood in a titration experiment yielded a linear PCR signal over a range of 3 orders of magnitude. The TaqMan-based PCR assay for C. albicans exhibited a low limit of detection (5 CFU/ml of blood) and an excellent reproducibility (96 to 99%). While the C. albicans species-specific probe had 100% specificity for C. albicans, all Candida genus-specific probes cross-reacted with other organisms likely to coinfect patients with C. albicans infections. On the basis of these data, we determined the C. albicans loads with a species-specific probe from 122 blood samples from 61 hematology or oncology patients with clinically proven or suspected systemic Candida infections. Eleven positive samples exhibited a wide range of C. albicans loads, extending from 5 to 100,475 CFU/ml of blood. The sensitivity and specificity of the present assay were 100 and 97%, respectively, compared with the results of blood culture. These data indicate that the TaqMan-based PCR assay for quantitation of C. albicans with a species-specific probe provides an attractive alternative for the identification and quantitation of C. albicans rDNA in pure cultures and blood samples.Invasive candidiasis, a common cause of nosocomial infection, is a leading cause of infections among patients receiving bone marrow transplantations or those with leukemia or other cancers and is also associated with a high rate of morbidity and mortality (10,18,22). Given the rapidly fatal course of candidiasis, there is a need for improved methods for early diagnosis and subsequent initiation of antifungal therapy in order to have a significant impact on the death rate (1, 12). One such improvement is the application of rapid and sensitive methods based on PCR that enable the amplification and quantitation of a broad range of fungal pathogens directly from specimens and pure cultures.Two quantitative real-time PCR systems have been described for Candida detection. An assay based on the PCR LightCycler system (Roche Molecular Diagnostics Systems, Indianapolis, Ind.) was applied by Löeffler et al. (15) for quantification of Candida albicans DNA in blood to which known numbers of blastoconidia had been added. Those investigators also used the assay to determine the fungal burdens in a small number of blood samples taken from patients with hematological malignancies. More recently, Guiver et al. (7) and Bowman et al. (3) described the automated detection of fungal DNA by using the TaqMan assay (Applied Biosystems, Foster City, Calif.) with clinical isolates and murine tissues, respect...