To evaluate methods for detecting pulmonary edema, pulmonary extravascular water volume was measured at 24 hour intervals (total 72 hours) in 25 patients with acute myocardial infarction. Measured lung water was compared with results of clinical, blood gas, X-ray and hemodynamic methods for detecting pulmonary edema. Increased pulmonary extravascular water volume on one or more measurements was observed in 18 of the 25 patients and was associated with an abnormal chest radiograph and increased pulmonary arterial wedge, pulmonary arterial diastolic and right atrial pressures. It was associated less well with clinical, blood gas and other hemodynamic measurements. Pulmonary arterial diastolic or pulmonary wedge pressure was a significant predictor of lung water 24 hours later. Both "preclinical pulmonary edema" and the "therapeutic phase lag" could be predicted from the pulmonary wedge pressure. Clinical, blood gas, radiographic and other hemodynamic measurements were not predictive.