The technique of hybridization of myeloma and B-lymphoid cells synthetizing antibodies, allows to obtain cellular clones producing a pre-defined antibody, during an undefined time and in unlimited quantity. The monoclonal antibodies have analytical properties which have never been obtained until now. They also constitute a major progress in the production of antisera, allowing their standardization, not only of place (unlimited production) but of time, thanks to the immortality (at least in principle) of the hybridoma clones. Finally, they represent a possible revival of serotherapy.