From the chair to the laboratories: Louis Henry and the professionalization of research in natural sciences in Belgium In 1869, Louis Henry (1843-1913), a well-known Belgian organic chemist, proposed a reform in order to include scientific research in the course of sciences studies at the Université Catholique de Louvain. He insisted mostly on the need of laboratory work for students, and on the crucial role of the Ph.D. thesis, based on original and personal research, worked out in the frame of a professor's laboratory. This reform, and the activity his author led his life through to promote his views about research at the university, is taken as an example of early professionalization of the natural sciences in Belgium. Four out of the six conditions pointed out by A.M. Carr-Saunders and A. Wilson (1933) are analysed in detail; the two others are indirectly addressed. They all lead to the conclusion that, although the ideas of 1869 only became reality about 1900 at the Université Catholique de Louvain and everywhere in Belgium, his reform and his attempts to achieve it in his own department constitute an important step to the professionalization of Belgian science.