Monoclonal antibodies are a relatively recent discovery--the first ones were obtained by Köhler and Milstein in 1975. The results obtained by these authors were published in the journal "Nature" under the title: "Continuous cultures of fused cells secreting antibody of predefined specificity". This title is almost a definition and contains all the elements involved in the problem. Monoclonal antibodies are obtained by applying a technique described in just a few pages (Thiry and Pastoret, 1981), but which combines many other techniques and is the fruit of the slow maturation of several fundamental biological problems. It is therefore impossible to present them out of this context. This article is comprised of two parts. The first, though far from being the most important, presents the problem and attempts to give the most exact picture possible of what a monoclonal antibody is. How is it obtained, what are its properties, of what use can it be? The second part attempts to describe present applications of monoclonal antibodies and to draw from this their prospects for the future, taking account of all the possibilities involved for Veterinary Medicine.