The classical theory of commerce encourages the liberalization of international trade on the grounds that this contributes considerably to the growth of welfare. This study sets out to explore this hypothesis empirically by analysing the relationship between external market openness and per capita GDP examined in twenty-two OECD countries between 1950 and 2000. The results bear out to support the existence of a positive correlation. The novelty of the study is that the author pays special attention to the temporal aspects of the interaction between openness and per capita GDP which can be characterised in terms of a nonstationary and nonlinear trend, as expected.