Exercise renography is an investigative procedure used to visualize a renal functional disturbance of essential hypertension (EH). The exercise protocol was developed to intensify a renal functional abnormality observed in standing hypertensive patients, when it appeared that this disturbance was directly associated with EH. Clearance determinations during light ergometric exercise showed that the abnormal scintigraphic images of the exercise renogram result from a prominent contraction of glomerular filtration rate (GFR), while effective renal plasma flow (ERPF) remained comparatively stable. The results obtained at present with exercise renography and clearance determinations suggest that afferent-efferent glomerular vessel dysfunction disrupts the stable relationship between GFR and ERPF in EH. This relationship is severely disturbed, and most readily recognized, during exercise. It is suspected that this functional abnormality results in the activation of the renin-angiotensin axis. A particularly exciting consequence of this research is the recognition that scintigraphy permits recognition of a disruption of the stable relationship of GFR and ERPF. This opens the door to a broad area of research unrelated to EH, since initial results in renovascular disease and urinary tract obstruction indicate that the fixed relationship between GFR and ERPF can be disturbed in these and other diseases as well.