BACKGROUND: Diagnosis of ventilator-associated pneumonia (VAP) is difficult. The usefulness of high-sensitivity procalcitonin (ProCa-S) and high-sensitivity C-reactive protein (CRPH) in bronchoalveolar lavage (BAL) fluid and serum in the prediction of VAP was determined. METHODS: The study was conducted over a 28-month period (November 1999-June 2002) at the University Hospital Maastricht. BAL fluid samples were collected from patients admitted to the intensive care unit. Differential cell count and quantitative culture of BAL fluid were performed. C-reactive protein (CRP) and procalcitonin (PCT) on BAL fluid were determined by means of two high-sensitivity kits (CRPH and ProCa-S, respectively). Since both kits were designed for use on serum, validation for use on BAL fluid was performed. RESULTS: A total of 117 patients were included. 43.6% (51/117) had microbiologically confirmed VAP. Both CRPH and ProCa-S showed good matrix effect, linearity and intra- and inter-assay variation. No significant differences in PCT and CRP concentrations in serum and BAL fluid were found between the VAP and the non-VAP group. CONCLUSIONS: Both the ProCa-S and the CRPH kits can be used for assessing the concentration of PCT and CRP in BAL fluid, respectively. PCT and CRP concentrations in BAL fluid appeared to be of no additional value in the diagnosis of VAP.