The accumulation of excess lung water is a major concern after the infusion of large amounts of crystalloid solution. The parameters used to monitor total body and lung water balance include changes in body weight, and the measurement of pulmonary vascular and plasma colloid osmotic pressures. We studied the reliability of these parameters in predicting lung water during severe fluid overload in nephrectomized sheep. We found that the normal lung appeared resistant to excess fluid accumulation, particularly when compared to the splanchnic circulation. Body weight change was an unreliable index of lung water with a correlation coefficient of 0.43. Pulmonary vascular pressures were the best index (r = 0.83) with lung water accumulating rapidly after capillary pressure exceeded 30 cm H2O. The difference between pulmonary capillary pressure and plasma colloid osmotic pressure was not as reliable (r = 0.72) as was capillary pressure alone.