Background: The lung protecting effect of propofol requires methods to measure the propofol concentration of the epithelial line fluid covering the alveolar surface.We hypothesized that (1) propofol can be determined in bronchoalveolar lavage (BAL) by reversed phase high performance liquid chromatography with fluorescence detection. (2) Positive end-expiratory pressure (PEEP) ventilation may have an effect on propofol concentration in BAL (cpB). Methods: 76 surgical patients were investigated after institutional review board approval. After criteria-based exclusion 45 samples were included. For group I (n=15) BAL was performed directly after induction, for group Z (n=15, PEEP=0cm H2O) and P (n=15, PEEP=10cm H2O) at the end of anaesthesia. BAL and plasma samples were analysed for propofol by reversed phase high performance liquid chromatography with fluorescence detection. Data from all groups were compared by non-parametric Mann-Whitney U-test. Results: Propofol can be detected in BAL. CpB varied between 23 and 167μglμ1 in all groups. Patients ventilated with PEEP (group P) showed significantly higher cpB (median 74.5μglμ1) compared to those immediately after induction of anaesthesia (median 42.0μglμ1) (group I), but not to those ventilated without PEEP in group Z (median 52.5μglμ1). Conclusion: Epithelial line fluid, sampled by BAL, can be used to determine cpB by reversed phase high performance liquid chromatography with fluorescence detection. Continuous propofol infusion and PEEP ventilation may have an effect on cpB.