The increasing importance of IT rose to the top of list of marketing managers` key concerns and IT has been used widely in performing various marketing activities and decisions. However, little was known about how to employ IT in various marketing activities and how to use IT as a strategic marketing means. Also, comprehensive empirical studies have rarely been conducted. This study examines the effectiveness of integrative use of marketing and IT. More Specifically, this study attempts to identify the factors that influence the effectiveness of marketing information systems. The manufacturing firms listed in the Korean Stock Market were surveyed. The major findings of this study are as follows. First, the variables of organizational characteristics such as formalization of decision making, cooperation between marketing function and IS function, and degree of decentralization were significantly related to the success of marketing information systems. The variables of user characteristics such as age, computer knowledge, and marketing knowledge were also highly associated with the success of marketing information systems. Second, it was also found that the support capability of marketing information systems is the major factor of the effectiveness of marketing information systems. Third, the variables such as age and marketing knowledge of marketing managers, cooperation between marketing function and IS function, and ratio of export sales to total sales were found to be the major factors to strengthen the competitiveness of firms, Fourth, three variables such as marketing knowledge of marketing managers, cooperation between marketing function and IS function, and various support capabilities of IS were the main factors to affect the users` satisfaction with the information systems. These results imply that, in order to increase the effectiveness of marketing information systems, a firm should enhance a cooperation between marketing function and IS function, diversify the support capability of IS, and strengthen the computer mind and computer knowledge of end-users.