Résumé : This paper revisits the literature providing empirical evidence that patent offices are biased in favour of their national applicants. If true, this “national bias” would be proof of disrespect of several international patent-related treaties. Existing investigations are however subject to an important limitation: they focus only on grant rates – a potentially biased indicator of stringency, since it is influenced by economic forces. It is argued that including a deeper analysis of how the patent examination process is carried out provides a more robust approach. Relying on a unique database of 2400 patent families filed simultaneously in three patent offices (EPO, JPO & USPTO), the paper finds no evidence of national bias throughout the examination process of any of them.