The paper contributes to the ongoing discussion of uneven development and unequal exchange within development studies. The point of departure is the world system theory that attributes uneven development to an inherently deficient world political and economic structure. In this paper, we propose the concept of ‘social metabolism' and its operational tool, Material Flow Accounting (MFA) as a means to empirically illustrate the notion of ‘ecological' unequal exchange by tracking flows of matter in international trade. Using examples from developed and developing economies, we show that there is a net flow of materials and resources from parts of the periphery to the core to allow for surplus to accumulate, both in monetary and biophysical terms. However, we also demonstrate that this pattern cannot be generalised for all periphery and core countries; other factors, such as population density and available land area, play an important role as well.