One considers a model of accumulation of the human capital in the presence of the international migration offers. One shows that under certain conditions,this option can support the increase in the stock of the national human capital by taking of account the externalities. Thus the `brain drain' would have a positive impact on the national economy under a well controlled restrictive migratory policy. The difficulty of this control scheme leads us to propose an alternative model suggesting the internalisation of the human capital externalities thus allowing the implementation of the social optimum. The mechanism of this internalisation is based on the endogenous creation of cultural norm with the accumulation of the knowledge. This social norm avoids the risks of conditionalities inherent in a migratory policy as a mechanism of internalisation of the externalities of the human capital.