A technique was developed for separating total serum pentitols into individual arabinitol, adonitol and xylitol and determining their relevance for the diagnosis of disseminated candidiasis. Pentitols were separated as trimethylsilyl derivatives on two 25 m long, bonded methyl silicone columns with a 0.32 mm i.d., and quantified by selected ion monitoring of their protonated molecular ions obtained in chemical ionization. The 173 samples studied were divided into culture-positive, culture-negative, and no-culture groups. Twelve percent of all samples were false positives by the total pentitols method due to increased adonitol and/or xylitol. The continued use of the total pentitols method is, nevertheless, recommended because of its convenience; however, samples with increased total pentitols (and normal creatinine) should be reanalyzed for individual pentitols. Increased arabinitol and normal creatinine are indicative of candidiasis even when blood cultures are negative.