Within a general equilibrium framework of a developing economy with a foreign owned factor of production, this paper questions whether the informal-formal sector relationship is pro-cyclical/ complementary – expansion or contraction in one necessarily implies an expansion or contraction in the other – when the informal sector is subject to a technological shock. We derive a necessary and sufficient condition under which a positive shock to the informal sector results in a contraction in both the size of the urban formal sector and the informal sector. Thus, although our result shows that the informal-formal sector relationship is pro-cyclical, it nevertheless calls into question the conventional wisdom on the benefits of intervention in the informal sector of developing economies, particularly where multinational corporations sub-contract certain labor intensive stages of production to the informal sector.