Changes in blood pressure, blood non-protein nitrogen, albuminuria, urinary concentration, PSP excretion, urea clearance, glomerular filtration rate, renal blood flow and filtration fraction were followed with advancing age in normal subjects, patients with chronic nephritis and patients with essential hyperrension.Gradual decrease of renal function was generally observed. Except the concentrating ability which showed more marked decrease with age than normal in both nephritis and essential hypertension, the decrease of renal function with advancing age was more pronounced inpatients with chronic nephritis than in normal subjects or patients with essential hypertension.