An aqueous extract of Pleurotus sajor-caju was found to have a hypotensive effect in rats. Intravenous infusion of the extract into rats caused a decrease of the mean systemic blood pressure in a dose dependent manner. A typical dose of 25 mg of the extract decreased the mean systemic blood pressure from 110 mm Hg to 70 mm Hg. The systolic and diastolic pressure changed proportionally with minimal alteration in heart rate. The hypotensive effect of the extract was not due to its major electrolyte content because a solution reconstituted with the same electrolyte composition had a transient pressor effect rather than lowering the blood pressure. The same extract was also found to affect renal hemodynamics such that it caused a decrease in the glomerular filtration rate by more than 50% after 120 minutes. The effect did not seem to be mediated through changes in systemic blood pressure.