The first part of this article is a revue of the bibliography which gives the main data on nornicotine (reaction of conversion). It is widespread in the Nicotiana genus but its presence is often considered as a cause of defect in industrial tobacco. Effectively, it gives a taste to smoke which is very little appreciated as it transforms in myosmine during combustion. In the leaves, nornicotine is produced, in situ, that which appears in the roots does not migrate. In the presence of nornicotine the oxidation of polyphenols produces a red color : it is the origin of cherry red spots seen in certain flue-cured tobacco. In the second part of the report some work carried out at the tobacco Institute of Bergerac (ITB) is given. First of all, two methods used to determine nornicotine are described. One using colorimetry is quick and used for screening purposes, the other, by HPLC, is more precise and permits the determination of all the alkaloids. Afterwards, the existence of genetic variability is shown for the nornicotine content in two varieties considered to be fixed and in the sub-population of one of these. Finally the authors report on the methods used by the ITB to eliminate NN character during selection and to control the quality of tobacco seed (cotyledon-test, certificate of conformity).