Multiagent systems (MAS) are spreading, in the academic world as well as in industry. Nevertheless, MAS design is still a problem. The agent community now has some experience. So, we considered existing techniques allowing formalisation and reuse of the experience. We particularly considered object-oriented techniques, for they are close to the MAS paradigm, for they are widely used to implement MAS, and for they are strongly integrated in the computer science world. So we develop through an example the idea of using patterns to describe the usage of existing models and techniques in MAS domain.