The takeover of the Bolivian presidency by the peasant trade-unionist Evo Morales and his party, the Movement towards Socialism (MAS), in 2005 not only marked the return of the left into the national political arena, but illustrates as well the raise, begun in the mid 90s, of the peasantry as an autonomous protagonist of Bolivian politics, in a context of growing urbanisation. This article focuses on the political and social conditions prior to the electoral triumph of MAS in a supposedly hostile environment: the cities. On the basis of an ethnographic research carried out within the working-class districts of La Paz, this work aims to show how a particular partisan configuration that favours its rural membership acts as a constraint for the party’s implantation in urban areas. Nevertheless, this fact does not turn into an obstacle, mainly due to the control that MAS holds on public jobs, which plays a key role in maintaining internal discipline in the cities.