In France there is presently an increasing development of horizontal mergers between companies belonging to the same field. In this paper we shall study only the mergers which occur in the mass consumption field, due to the following reasons: - Existence of a common distribution with very concentrated buying centers working for the account of a very scattered net work of point of sales; - Nature of buying process (the buyer being generally the housewife) . - Similitude of marketing technics (sales force, promotion, advertising). The mergers set many marketing problems. Here marketing must be defined in its most general meaning as the basic philosophy of the developing companies, that is a new structure, a new arrangement of forces in order to face new development of the market better with a greater efficiency. We take in this paper examples of several horizontal mergers recently achieved in the food field in outlining the problems raised by short term evolution of the group.