Renal function studies have been carried out in both the recumbent and in the oblique position in 2 cases of orthostatic hypotension. In both cases a definite fall in plasma flow and glomerular filtration rate took place, but this occurred only after registration of a considerable fall in blood pressure.The filtration fraction remains unchanged after the fall in blood pressure. The extraction ratio remains unchanged after a considerable fall in blood pressure.The data may indicate that the renal function becomes normal if blood pressure is kept on a low level over a fairly long period. However, further observations are required before any definite conclusion may be drawn.