As a reaction to changes in environmental factors and in their customers? purchasing behavior many suppliers in the business-to-business field have introduced key account programs. The aim of these programs is to serve strategically important customers in a more individual manner than minor accounts. A core assumption in the key account literature is that supplier companies are willing to increase their input into important customer relationships because they hope to enhance the relationship outcome. This paper presents the results of an empirical study among 297 purchasing managers in which this assumption was tested. Based upon the relational exchange framework, the authors analyze whether key accounts receive more relational treatment than ordinary accounts (input side). On the output side this research examines whether key customers perceive relationship quality (satisfaction, trust, commitment) to be better than non-key accounts. Key words: Key account management, relational exchange, perceived relationship quality, customers' perspective.