Intravenous administration of furosemide in the horse resulted in an immediate and significant decrease in right atrial pressure, pulmonary arterial pressure, pulmonary arterial wedge pressure, cardiac output, and stroke volume (P less than 0.05). There was a significant increase in total systemic vascular resistance and heart rate (P less than 0.05). There were no significant alterations in mean arterial pressure. Coincidental with these hemodynamic changes were increased urine production and associated increase in packed cell volume and total serum protein. All variables except cardiac output, stroke volume, packed cell volume, and total solids returned to base line levels within 105 minutes after furosemide was injected. It is suggested that the effects of intravnously administered furosemide in the horse are transitory and dependent upon the decrease in plasma volume from diuresis.