From a panoramic and comparative perspective, the article aims at reviewing the framework of regional and national planning in Brasilia and Venezuela's Ciudad Guayana, while exploring their relationship with political and economic goals in the heyday of Latin America's modernism and desarrollismo (developmentalism). Although these projects have often been addressed in terms of their architectural value and urban design, this article's approach stresses their relationship, on the one hand, with national processes of industrialization and urbanization, and on the other, with regional models of development, already tested on the continent. Such an approach requires, firstly, the contextualization of Latin America's growing corporate states after the Second World War, while exploring the relationship with national apparatuses of North American-orientated planeamiento that progressively replaced the urbanismo fostered by European traditions since the 1920s. The case of Brasilia is explained through the image of its original sin, in the sense that the city did not result from proper regional planning, a shortcoming that eventually reduced its capacity for adapting new functions and settlements to the original Pilot Plan. Ciudad Guayana's main hindrance was instead its feet of clay; in addition to the weakness of the industrial activity in the long term, both Puerto Ordaz and San Felix were remotely planned, without much attention paid to their integration and the absorption of the informal population.