Serum is the blood component that is obtained after coagulation and removal of cellular components. Besides serum proteins, it contains, e.g. growth factors, amino acids, and hormones. This complex mixture makes serum one of the most important supplements supporting the cells growth and proliferation for in vitro cell culture. Of special interest is the Fetal Bovine Serum (FBS). It is especially rich in growth factors and is particularly low in antibodies that may negatively influence the cell culture work. It supports most cell lines and undergoes strict quality controls. FBS is processed through protein A-Sepharose columns to reduce the IgG content of serum to below 5 µg/ml. This process is gentle to the product and ensures an unimpaired growth promotion. The specially treated FBS has a very low IgG antibody concentration and is outstandingly suitable for hybridoma cell culture. Thereby, the IgG stripped FBS facilitates the purification of monoclonal antibodies.