The labor income share in national income is a good indicator of the extent to which the working classes are able to reap the fruits of economic growth or, conversely, bear the burden of economic stagnation. This paper aims to reconstruct the labor income share of Argentina, Brazil and Mexico in a three-sector framework, including the rural, the urban formal and the urban informal sectors. We find that in all three countries the share of labor earnings peaked in the middle of the 20th century. Fluctuations in the Brazilian and Mexican labor income shares were large, with a sharp decline in the post-1961 and post-1976 periods, respectively. In Argentina, the labor income shares tended to be more constant at levels around 50 per cent, testifying to a more stable and egalitarian distribution of income.