Histological stains are commonly used to make cell structures more readly visualized than in unstained specimens. They serve to reveal structural compounds and differences during evolution or in pathological conditions. Classical histological dyes possess only restricted specificity depending on the their selectivity to bind with cellular components. The demand for highly specific stainings of molecules at the cellular level has initiated the development of dedicated probe techniques. Such techniques are either of histochemical nature or they are based on specific ligand bindings and involve f.e. polyclonal/monoclonal antibodies, lectins and nucleotides. For the location of those bindings appropriate detection systems must be used.