The Church of Pius XII was faced with the major problem of secularisation that accompanied the modernisation of European society. In the post-World War II Catholic world, France and Belgium were pioneers in seeking new pastoral methods that could reach out and involve, in particular, the workers, that social class which was most sensitive to the dynamics of de-Christianisation and religious indifferentism. The relationes ad limina of the period allow us to reconstruct a lively and innovative ecclesial landscape, within which the experience of worker priests was the best-known and most debated pastoral response, but not the only one. This article describes this tendency towards pastoral experimentation in France and Belgium between 1947 and 1957, at a time when Pius XII seemed to view Progressismus gallicus with fear and concern, but also with some hope.