['To determine the concentration of parathyroid hormone-related protein (PTHrP; an autocrine/paracrine regulator of type-2 alveolar epithelial cells proliferation and apoptosis) in the epithelial lining fluid (ELF) from patients without pulmonary disease and from patients with acute lung injury (ALI), and to evaluate whether PTHrP concentrations correlated with the intensity of lung injury.', 'Prospective study.', 'An adult trauma/surgical ICU in an urban teaching hospital.', 'A total of 20 patients with ALI receiving mechanical ventilation (patients), and 10 patients without pulmonary disease not receiving mechanical ventilation (control subjects).', 'None.', 'PTHrP was detected in all BAL fluids, and ELF PTHrP concentrations (median; 25% to 75% percentiles) tended to be higher in patients (52.2 nmol/mL; 20.8 to 65.6 nmol/mL) than in control subjects (25.4 nmol/mL; 20.5 to 35.4 nmol/mL; p = 0.18). In patients, ELF PTHrP concentration correlated positively with the PaO(2)/fraction of inspired oxygen ratio (r = 0.53; p = 0.005), and negatively with lung injury score (r = - 0.44; p = 0.02), radiologic score (r = - 0.40; p = 0.04), and BAL albumin concentration (r = - 0.42; p = 0.02).'] Does parathyroid hormone-related protein in epithelial lining fluid in humans negatively correlate with the severity of lung injury?