The Common Agricultural Policy (CAP) is a very complex area of the European integration. As agriculture (especially agricultural trade) plays a very important role in the Hungarian economy, agricultural adaptation and its competitiveness is a crucial question for the whole economy. It is worth then examining how market players are expected to respond to new market challenges. In order to reveal some competitive effects of CAP adaptation, I turned to customs union (CU) theories, focusing on the possible theoretical production and consumption reactions. Finally the relevance of these presumptions to Hungarian agricultural accession is explored, revealing certain competitive effects.