The function of polygonal liver cells can be estimated by using liver specific dyes such as labelled BSP or bengalrosa and labelled X-ray contrast media. Various methods are available: clearance with blood counting or external monitoring, whole body clearance and retention measurement. These tests are of value for following the course of liver diseases. Blood flow measurements either with labelled colloids or 133 Xe are mainly used for scientific purposes. Portosystemic shunts can be detected by injection of labelled microspheres in the spleen and lung monitoring or scanning. With the dynamic scintigraphy portosystemic shunts can be visualized ( radionuclide splenoportography). The measurement of the praecordial appearance time after rectal instillation of 133 Xe permits the functional evaluation of a surgical portosystemic shunt. Dynamic scintigraphy makes possible the estimation of the arterial part of liver blood flow after i.v. injection of 99m Tc and this together with the radionuclide splenoportography allows the assessment of disturbed blood flow in patients with portal hypertension. I. v. applied parathyroid hormone increases the arterial hepatic blood flow. Preliminary results indicate that patients with portal hypertension and a good response to parathyroid hormone seem to have a good prognosis after shunt operation. The determination of red cell survival with 51 Cr is helpful in the differential diagnosis of jaundice. The specificity of liver scanning with labelled colloids for malignant diseases can be reasonably increased by additional 67 Ga-scintigraphy. In the diagnosis of hepatoma with both colloid and Galliumscan and the evaluation of alpha-fetoprotein a 90% accuracy can be achieved. The hepatobiliary transport can easily be visualized with 99m Tc labelled IDA-compounds and also in patients with severe jaundice where the X-ray cholangiopathy is impossible. This examination is indicated in patients with bile duct observations (also intrahepatic), after cholecystectomy, for the differential diagnosis of jaundice, for the demonstration of refluxes etc. The most important radioimmunological in vitro methods for the investigation of liver diseases are only briefly described.