Framing plays an important role in lobbying, as interest groups strategically highlight some aspects of policy proposals while ignoring others to shape policy debates in their favour. However, due to methodological difficulties, we have remarkably little systematic data about the framing strategies of interest groups. This article therefore proposes a new technique for measuring interest group framing that is based on a quantitative text analysis of interest group position papers and official policy documents. We test this novel methodological approach on the basis of two case studies in the areas of environmental and transport policy in the European Union. We are able to identify the frames employed by all interest groups mobilised in a debate and assess their effectiveness by studying to what extent decision-makers move closer to their policy positions over the course of the policy debate.