Abstract Pleural inflammation underlies the formation of most exudative pleural effusions and the plasma kallikrein-kinin system (KKS) is known to contribute. Mesothelial cells are the predominant cell type in the pleural cavity, but their potential role in plasma KKS activation and BK production has not been studied. Bradykinin concentrations were higher in pleural fluids than the corresponding serum samples in patients with a variety of diseases. Bradykinin concentrations did not correlate with disease diagnosis, but were elevated in exudative effusions. It was demonstrated, using a range of primary and transformed mesothelial and mesothelioma cell lines, that cells assembled high molecular weight kininogen and plasma prekallikrein to liberate bradykinin, a process inhibited by novobiocin, a heat shock protein 90 (HSP90) inhibitor, cysteine, bradykinin and protamine sulphate. Of the common plasma prekallikrein activators, mesothelial cells expressed HSP90, but not prolylcarboxypeptidase or Factor XII. Calcium mobilisation was induced in some mesothelium-derived cell lines by bradykinin. Des-Arg(9)-bradykinin was inactive, indicating that mesothelial cells are responsive to bradykinin, mediated via the bradykinin receptor subtype 2. In summary, pleural mesothelial cells support the assembly and activation of the plasma KKS by a mechanism dependent on HSP90, and may contribute to KKS-mediated inflammation in pleural disease.