Purpose – Prime contractors spent a substantial part of their turnover on purchasing. The management of the purchasing function therefore has a large influence on the overall performance of a prime contractor. The more developed the purchasing function is, the greater its contribution to success of the companies. The purpose of this paper is to measure and explain the development in maturity of the purchasing function in construction firms. Design/methodology/approach – Based on a literature review, a theoretical framework for the assessment of purchasing maturity is provided first. Then a longitudinal multiple case study is executed in order to assess the maturity development of the purchasing function in seven construction companies. Results are compared with a historical baseline assessment. Findings – The results demonstrate an increase in the maturity of the purchasing function in general and in particular in the management of strategic relations. The case companies have reached a maturity in which they start to coordinate activities in their supply chains. Increased use of IT solutions enables a more integrated approach of the construction process. Practical implications – IT and in particular Building Information Modelling pave the path towards an integrated supply chain, which in turn enables the reduction of waste in the processes. Nevertheless, companies still struggle with the tension between project-based flexibility and long-term relations with suppliers. Originality/value – The development of purchasing maturity was measured in a baseline measurement and in a second assessment performed five years later by using the exact same model and exact same case companies.