The Internet, with its speed, agility, scalability and wide reach characteristics, can be used to create a wide and open business market, able to offer efficiency to the process of buying and selling products, reducing transaction costs. However, most e-commerce applications do not exploit the synergy of the Internet because they only involve a single enterprise with its own suppliers and customers. It is necessary to take the communication and cooperation idea to an environment that integrates virtual enterprises and buyers, allowing the creation of an agile and efficient electronic marketplace. With the goal of constructing an efficient and extensible marketplace, this article proposes an electronic marketplace architecture based on intelligent agents and knowledge, contemplating the search and aggregation roles of an intermediary. The process of medicine purchase and sale is used to exemplify the use of this architecture.