Peptides exist in all organisms, wherever there are cells. The range of their physiological functions is huge. Biologically active peptides can act as hormones, neurotransmitters, growth factors as well as toxins and antibiotics. This is what makes them highly interesting drug leads. They are used for the treatment of autoimmune diseases, cancer and other diseases. Despite some drawbacks, peptides are gaining in importance as candidates for drugs and fuelling interest in research into natural and synthetic peptides.