Ontogenic and genetic variations of nitrate reductase activity and nitrate content were studied in twelve species of Nicotiana tabacum from transplanting to harvest. All the varieties had similar nitrate reductase activity. Nitrate reductase activity was more influenced by soil and climatic conditions than genetic variability. It is therefore delicate to use it for perfecting the prediction of nitrate accumulation of an more or less early test. Otherwise the results show that nitrate accumulation is a varietal phenomenon at the end of the growth. Burley varieties had the highest nitrate contents. However other varieties such as PB D6 (dark tobacco) and NC PY (Virginia) accumulate less nitrate. The search for other potential progenitors should be carried out to set up a breeding program in order to reduce nitrate contents at the harvest. The reduction of nitrate content in tobacco as raw material depends for the moment of the variety, a light and early fertilization and a good knowledge of soil and climatic conditions.