The Reticuloendothelial System (RES) consists of cells descending from the monocytes which are able to perform phagocytosis of foreign materials and particles. 90% of the RES are located in the liver. The most important function of the RES ist phagocytosis, but it also takes part in cytotoxicity against tumor cells and has a function in the regulation of the immune system. The importance of the RES is obvious in diseases of the bile ducts. An obstruction can lead to a decrease in the function of the RES. Beside a mathematical model there are also a few experimental methods to measure the phagocytic capacity and thus the efficiency of the RES. They are based on a clearance study of the amount of particles absorbed by the RES. This study can e.g. be done with Nanocoll which has been marked with 99mTc. But instead of the bloody clearance, a scintigraphic study using a gamma camera can be performed. With that, the increase time, the liver extraction fraction and the steepness of increase can be determined. Such a test could be of clinical relevance as a parameter for the prognosis of patients with trauma, sepsis or shock. The function of the RES in the pathogenesis of the biliary pancreatitis could also be examined closer with the help of such a test. The requirements a test of the RES should meet are reproducibility, repeatability and practicability.