Renal and hemodynamic effects of furosemide were studied in 30 patients with acute myocardial infarction. When marked congestion of lungs was absent, the effects of furosemide were somewhat different from those of recent reports. The changes of pulmonary arterial pressure and wedge pressure were biphasic; there was first pressure rise in many occasions followed by reduced pressure; the latter is commonly believed to be the beneficial effect of furosemide. In these patients without marked congestion but in an acute state of myocardial infarction, within 5 min of furosemide administration, there was marked increase in urine volume, sodium and potassium excretion along with increases in creatinine clearance which is commonly found in the other conditions, but is in contrast to the recent reports on patients with acute myocardial infarction complicated with pulmonary congestion.