BACKGROUND: Procalcitonin (PCT) is a recently described inflammatory marker that has been shown to increase significantly in patients with severe systemic bacterial infections or sepsis. Reports on the diagnostic and predictive value of PCT in systemic fungal infections are limited. METHODS: In order to evaluate the role of PCT in systemic mycosis, 14 patients (mean age 40 years) with proven or probable systemic fungal infections were investigated. Blood samples were collected on days 1, 3, 5, and 10 after the onset of signs and symptoms of systemic fungal infection (clinical and/or laboratory diagnosis and/or radiographic evidence). PCT measurements were performed using an immunoluminometric assay. RESULTS: In five patients with severe fungal infection and an unfavorable course (patient group 2), PCT levels were moderately elevated on day 3 (0.5-1.0 ng/ml), whereas they were normal in the patients who recovered (patient group 1). High PCT levels (>/=1.11 ng/ml) were detected on the 10th day of the course of the illness in patient group 2. A normal or moderate elevation of PCT on day 10 was observed in patient group 1. The difference in mean PCT levels in patient groups 1 and 2 on days 3 and 10 were statistically significant. CONCLUSIONS: PCT levels seem to correlate with the severity and outcome of systemic fungal infection. If this finding can be confirmed in a larger number of patients, it could serve as a prognostic indicator.