For many years, the potential of immunoglobulin M (IgM) antibodies was not fully understood because of characteristics different to the well-known immunoglobulin G type like low target affinity, cross reactivity and complex protein structure. In the meanwhile IgMs have been positively evaluated for their use as therapeutic agent in the mucosal environment but also in serum to eradicate upcoming tumor cells and invading antigens. Therefore IgM class of antibodies will play a significant role in clinical applications but also diagnosis in the future. To evaluate the full potential of this kind of antibody molecules large amounts of high quality product will be needed. In this review the focus is set on the biotechnological aspect of producing IgM class antibodies recombinantly in mammalian cells. Current achievements in expression and purification of this molecule are highlighted and compared.