Open software platforms are a recent innovation in the healthcare sector to foster integrated care scenarios. An important quality feature to facilitate innovation and to create an active platform ecosystem is openness. The openness is strongly influenced by the interoperability potential of the platforms. Hence, the assessment of the interoperability potential is a crucial task for evaluating the quality of platforms. However, there is a need for methodological support fostering the evaluation of eHealth platforms. Based on a design science research approach, the article shows, how the Maturity Model for Enterprise Interoperability (ISO 11353-2) can be instantiated in the healthcare domain. We describe a quantitative evaluation model which operationalizes the evaluation process of eHealth platforms. The contribution purposes to improve the transparency and reliability of the evaluation process. Furthermore, the introduced approach reduces the dependence on an evaluation team and facilitates the implementation of assessments.