Purpose – Brands have traditionally been regarded as a key asset and a source of competitive advantage in purchasing decisions, as customers are expected to prefer stronger brands to minimize risks. However, the role of brands in business markets is unclear and underresearched. The purpose of this study is to analyze the relevance of brands in a business-to-business (B2B) purchase setting and their key determinants. Design Methodology/approach – A research model was developed to explain brand relevance when compared with other decision factors in a B2B context. Based on the frameworks developed by Zablah et al. (2010) and Mudambi (2002), the model considers the purchase situation, decision-maker characteristics and firm size as determinants of brand relevance in the decision-making process. One of the most prominent Portuguese construction groups, which comprised three companies, was chosen for the sample of this study. Data were collected through a self-administered, online, cross-sectional survey, resulting in a convenience sample of 87 decision-makers. Findings – Findings suggest that attributes related with brands matter even in B2B rational decision-making processes. However, brands are not important to all organizational buyers or in all situations. Different purchase situations and decision-maker characteristics proved to have an impact on brand relevance, namely, brand reputation, prior purchases and brand awareness. Only firm size was not confirmed as a determinant of brand relevance in the B2B purchasing process. Originality/value – B2B brand research is scarce, especially for industrial services. By investigating the determinants of brand relevance in a B2B purchasing context, namely, in a construction services setting, this study contributes to bridging this literature gap. Moreover, the few studies on the subject have been largely descriptive in nature and managerially oriented, while this investigation emphasizes hypothesis testing through a proposed research framework. Also, in managerial terms, identifying determinants of the importance given to brands by organizational buyers is critical in deciding when investment in brand development is more likely to payoff.