The aim of the this paper is to analyze the effect that immigration has on the technology adopted by firms of the host country and on natives’ human capital. we will show that in a framework where labour market is characterized by random matching and costly search, social increasing returns may arise. In such a case, it is possible to demonstrate that there exists a strong and a positive interrelationship between some important features of the host economy, such a physical and human capital investments of natives and human capital of immigrants