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(PN) and a combined group (PN+ARDS).In all patients with ARDS and/or PN, markedly elevated BAL levels of IL-6 and IL-8 were detected, which were significantly greater than levels in CPO and healthy controls. Absolute quantities and time-course of these cytokines did not differentiate between the absence and presence of lung infection, or different categories of PN. Similarly, circulating IL-6 levels were comparably elevated in patients with ARDS and/or PN, whereas circulating IL-8 concentrations were inconsistently increased. TNF-α was rarely detected in BAL samples, but increased serum concentrations were measured in ARDS and/or PN patients.Bronchoalveolar lavage levels of interleukin-6 and interleukin-8, but not tumour necrosis factor-α, and serum concentrations of interleukin-6 are consistently elevated in acute respiratory distress syndrome and/or severe pneumonia, discriminating these entities from cardiogenic pulmonary oedema. Alveolar and systemic cytokine profiles do not differentiate between acute respiratory distress syndrome in the absence of lung infection and states of severe primary or secondary pneumonia, which evidently present with comparable local and systemic inflammatory sequelae.