This study was performed to determine whether the absorption of liquid from the lungs of postnatal sheep is dependent on pulmonary perfusion pressure, blood gases or blood flow. Relationships between perfusion pressure, rate of lung liquid absorption and perfusate PO2, PCO2 and pH were examined by linear regression analysis from in situ perfused lungs from sheep aged 6 weeks to 6 months. The airspaces of the lungs were filled with liquid containing an impermeant tracer, to allow measurement of the rate of liquid absorption. There was no significant relationship between the rate of lung liquid absorption and pulmonary blood flow (n = 36, r = -0.01, P > 0.1), pulmonary perfusion pressure (n = 36, r = 0.28, P > 0.05) or perfusate PO2, PCO2 or pH. No significant relationships were found between pulmonary blood flow and perfusate PO2, PCO2 or pH. There was no evidence to suggest that the absorption of liquid from the lungs of postnatal sheep is dependent on pulmonary blood flow, blood gases or perfusion pressure, within the limits studied, indicating that lung liquid absorption is dependent on the pulmonary epithelium and not on the pulmonary vasculature. The findings that lung liquid absorption continues in hypoxic environments and despite severe reductions in blood flow may be relevant to the field of transplant surgery. Experimental Physiology (2001) 86.3, 391-398.