The suggestion from post-mortem studies that there is an age-related fall in liver weight has been confirmed by in vivo studies, employing ultrasound or CT scanning. These demonstrate an estimated 28% lower volume in individuals above the age of 65 compared with those under 40 years of age. The functional significance of the fall in liver size with age is confirmed by the highly significant correlation between age, liver volume estimated by ultrasound and galactose elimination, the clearance of which is determined by functional hepatic mass this fall in mass of functional hepatocytes is also illustrated by an age-related reduction in binding of radiolabelled galactosyl-albumin. Liver blood flow, estimated by pulsed echo-doppler, or functional hepatic flow measured by the hepatic clearance of D-sorbitol or indocyanine green, falls significantly with aging, with around a 33% fall between youth and old age., The thickening of the sinusoidal endothelial lining with collagen, and fall in endothelial cell fenestrations, noted with increasing age in human liver, is likely to impair blood flow through liver sinusoids and hepatic perfusion, and reduce oxygen-dependent hepatocyte function, such as uptake of macromolecules. This may contribute to the link between the aging process and disease susceptibility.