The mainstream economy poses the opinion that a competitive advantage lies in resources, and, consequently - in competences as well - being a share of a single company and remaining under its sole control. Recently, some researchers (e.g. Castaldo, 2007; Lavie, 2006) have revised that approach and tend to emphasise the role of other sources of competitive advantage in business strategy, which embrace new, intangible assets. Such assets are being born and developed only within the inter-firm relationships built in network environment. Thus, the presented paper focuses on relational-based approach towards gaining relational rent. It aims at discussing the sources of an appropriated relational rent and, presenting - after Lavie, a new types of rent extracted from alliance networks. Next, the author presents some empirical evidence from healthcare market in Poland. Inter-organizational relations represent the central level of analysis of the achievement of relational competitive advantage. Empirical results indicate the crucial role of trust and commitment in the market relationships. They are the key success factors which enable the service providers to build a differentiated market position. The researched organizations pose effective communication between the parties of the relationship and the satisfaction resulting from the mutual respect and recognition as the components of value offerings.