Abstract. This paper incorporates equilibrium unemployment caused by efficiency wages into a monopolistic competition model of trade. Worker effort is treated as an endogenous variable that depends on the optimizing behaviour of firms and workers. Opening up trade induces firms to demand greater worker effort and to cut the size of their workforce. This counteracts the positive employment effect due to entry of firms. Circumstances are indicated in which the two effects just balance, leaving aggregate employment unchanged. Trade unambiguously increases worker effort, thereby enhancing within-firm productivity.