The aim of this study was to determine the effect of aging upon liver volume and apparent liver blood flow in healthy man. Sixty-five subjects between 24 and 91 years of age were recruited. Liver volume was quantitated by a gray scale B ultrasound scan method. Apparent liver blood flow was determined from the plasma clearance of indocyanine green, based on an assumption of no change in hepatic extraction of the dye with age. A significant negative correlation was observed between age and both liver volume and apparent liver blood flow (p less than 0.001), whether expressed in absolute terms or per unit body weight. Similarly, a significant negative correlation was observed between apparent liver blood flow per unit volume of liver (liver perfusion) and age (p less than 0.005). The reduction in liver volume, apparent liver blood flow and perfusion may at least partly account for the decline in the clearance of many drugs undergoing liver metabolism which has been noted to occur with aging in man.