Four types of radionuclide investigations are described here: 99mTc-labeled red blood cell scintigraphy, colloid liver scintigraphy, hepatobiliary scintigraphy, and positron emission tomography with [18F]fluorodeoxyglucose. The role of nuclear imaging techniques in the diagnosis of liver diseases has changed in recent years and now compliments morphological imaging modalities by offering the unique ability to visualize function and metabolism. The studies described here are therefore rarely performed now by themselves for the delineation of secondary liver tumors. These radionuclide investigations are used principally to narrow the differential diagnosis of focal liver disease.