Technetium-99m (Tc) mebrofenin hepatobiliary scintigraphy (HBS) enables a quantitative assessment of liver function. This is normally performed in a fasting state and might therefore reflect the resting liver function. We evaluated the change in liver function using HBS after stimulation with an oral metabolic challenge. Healthy volunteers aged 50-60 (n=12) or older than or equal to 75 (n=12) years underwent two sequential HBS. The first scan was performed after an overnight fast and the second scan was performed after the administration of chocolate milk. Hepatic Tc-mebrofenin uptake rate (cMUR) was calculated and the difference was expressed as percentage. cMUR after fasting was 10.9±2.5%/min/m (mean±SD) and increased by 20% to 13.0±3.1%/min/m after stimulation with chocolate milk (P<0.001). cMUR increased markedly after the administration of an oral metabolic challenge in comparison with fasting. This may be a consequence of hepatocyte stimulation, reflecting the hepatic functional reserve capacity.