In the transition of the national economy of the Slovak Republic ''new rules of game'' have been worked out for firms. Centralized economic management was replaced by independent business units' decisions. Under these conditions a firm must behave in such a way as to assure some prosperity for itself. The crux of the problem lies in the fact that market means a big unknown factor for the time being. The firms are badly missing decision criteria to meet the market requirements, firm's development plans, as well as marketing plans. The scope of information on the present market is also insufficient. And this is what makes the firms unable to develop their business activities in the right way. Nowadays the business units must accept for their working basis the needs and wishes of those determining their outputs (products, services, ideas, etc.). Present development makes it clear that the most important part of marketing became market research, the firm's policy concerning products, prices, sales and communication; changes in the present modern marketing reveal themselves - beyond other factors - just in the character of these partial activities. To obtain the level of a going concern depends on the fact how the firms succeed in jointing the above indicated marketing activities in a single programme and that's why the firms establish a marketing department. To ensure a successful working of such a department, the authors of the paper characterize: position of a marketing department in organizational structure of the firm; structure of the marketing department and some alternatives of its organization; activity of marketing department; marketing department staffing; principles of successful establishment of a marketing system in a firm.