We assess whether the distinction between old and new social movements still holds by examining the social class and value orientations of participants in old and new social movement protests. We argue that new cleavages have emerged from globalization, affecting not only electoral politics, but also contentious politics, and thereby having a homogenization effect on the structural basis of movements of the left. Moreover, we hypothesize that traditional cleavages, such as class mediate the homogenization effect of new cleavages. We look at participants in May Day and climate change demonstrations in Belgium and Sweden, two countries that differ in terms of strength of class cleavage. Results show that there is evidence of homogenization between old and new social movements and that this effect is more important when the class cleavage is stronger.