BACKGROUND There is a great number of agents involved in the acute respiratory distress syndrome (ARDS) physiopathology, and some of them may have a prognostic value. The objective of the present study has been to analyse the prognostic value of eicosanoids in this syndrome. METHODS A prospective study with 21 consecutive ARDS patients admitted to the intensive care unit of a therapy hospital in Barcelona, Spain, was carried out. In the first 48 h of the ARDS diagnosis, at baseline, the plasma levels, (in peripheral arterial and pulmonary arterial samples) of thromboxane B2 (TXB2), prostaglandin F1-alpha) (PGF1-alpha) and leukotriene B4 (LTB4) were analysed by RIA. Simultaneously we measured different pulmonary and systemic hemodynamical variables, as well as the pulmonary gas exchange data. We also studied the venous levels of the same eicosanoids in 17 healthy adults, used as reference. RESULTS Plasma levels of eicosanoids in the ARDS patients were higher than reference subjects (p < 0.05). No differences were observed between systemic arterial and pulmonary arterial values. From all the eicosanoids, only LTB4, (in both systemic arterial and pulmonary blood), was correlated with LIS (r = 0.49, p < 0.05; and r = 0.45, p < 0.05, respectively). Patients who did not survive presented a lower systemic-pulmonary arterial gradient of eicosanoids levels than survivors (-1.27 vs -0.10 ng/ml; p < 0.01). CONCLUSIONS In our ARDS patients only LTB4 plasma levels correlated with the severity of respiratory failure. Patients who did not survive presented a lower LTB4 gradient than survivors.