The historiographies of Mexico and Brazil have implicitly stated that business networks were crucial for the initial industrialization of these two countries. Recently, differing visions on the importance of business networks have arisen. In the case of Mexico, the literature argues that entrepreneurs relied heavily on an informal institutional structure to obtain necessary resources and information. In contrast, the recent historiography of Brazil suggests that after 1890 the network of corporate relations became less important for entrepreneurs trying to obtain capital and concessions, once the institutions promoted financial markets and easy entry for new businesses. Did entrepreneurs in Brazil and Mexico organize their networks differently to deal with the different institutional settings? We examine whether in Mexico businessmen relied more on networks of interlocking boards of directors and other informal arrangements to do business than in Brazil. Our hypothesis is confirmed by three related results: (1) the total number of connections (i.e., the density of the network) was higher in Mexico than Brazil; (2) in Mexico, there was one dense core network, while in Brazil we find fairly dispersed clusters of corporate board interlocks; and most importantly, (3) politicians played a more important role in the Mexican network of corporate directors than their counterparts in Brazil. Interestingly, even though Brazil and Mexico relied on very different institutional structures, both countries had similar rates of growth between 1890 and 1913. However, the dense and exclusive Mexican network might have ended up increasing the social and political tensions that led to the Mexican Revolution (1910–1920).