We viewed these results with great interest because we are also studying the role of PTHrP in lung injury. Two recent publications not cited in the article by Stern et al1support their hypothesis that levels of PTHrP in lung epithelial lining fluid correlate negatively with the development of lung injury. Speziale and coworkers2measured PTHrP levels in tracheal aspirates from newborn infants. PTHrP levels were significantly lower in aspirates from infants born at < 35 weeks’ gestation and with birthweights < 2 kg. In addition, PTHrP levels were significantly lower in male preterm infants compared to female and in preterm infants with respiratory distress syndrome. Furthermore, preterm infants exposed to steroids before birth had higher levels of PTHrP. Thus, PTHrP correlated with several indexes of lung maturation. In another study, Hastings and colleagues3 assayed PTHrP levels in BAL fluid from patients undergoing pulmonary thromboendarterectomy. Patients with lung injury developing following the thromboendarterectomy, based on Pao2/Fio2 < 300 mm Hg and the presence of bilateral lung infiltrates, had significantly lower BAL fluid levels of PTHrP than patients without lung injury. The difference was apparent preoperatively, before the insult occurred, suggesting that PTHrP might be a useful prognostic factor to predict lung injury in this model. Since alveolar type II cells are the major source for PTHrP in the adult and fetal lung, these two studies and the study by Stein et al,1 suggest that PTHrP in BAL fluid may be a measure of type II cell function.