In light of ongoing concern about commodity specialization in Latin America, this paper revisits the argument of Prebisch (1950) that, over the long term, declining terms of trade would frustrate the development goals of the region. This paper has two main objectives. The first is to clarify the issues raised by Prebisch and Singer (1950), as they relate the commodity specialization of developing countries (and Latin America in particular). The second is to reconsider empirically the issue of trends in commodity prices, using recent data and techniques. We show that rather than a downward trend, real primary prices over the last century have experienced one or more abrupt shifts, or "structural breaks," downwards. The preponderance evidence points to a single break in 1921, with no trend, positive or negative, before or since.