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. Embryonic stem (ES) cells are particularly demanding and it is crucial to keep them in their valuable undifferentiated state. When working with stem cells, maintenance of pluripotency and reduced differentiation are the main objectives. Historically, EC cell researchers had to laboriously screen several lots of serum to find one suitable for their cells. Capricorn Scientific offers ES Cell Pretested FBS to minimize the need for prescreening serum, saving both time and money while providing the assurance that the serum used has been screened by experienced ES cell culturists. The screening includes growth promotion, colony morphology, and cytotoxicity. ES Cell Pretested FBS is selected from our highest quality FBS lots and pretested on murine embryonic stem cells.