Fenamidone is a new fungicide, belonging to imidazolinone class, exhibiting a high level of activity against a range of Oomycetes disease such as grape, vegetable and tobacco downy mildews. It also controls a number of other pathogens comprising Ascomycetes and Alternaria spp . At the biochemical level, fenamidone inhibits mitochondrial respiration by blocking electron transport at the level of ubihydrossiquinone: cytochrome c oxidoreductase. This active ingredients has been developed only in mixture with other fungicides having different mode of action. In this work we report a study on the efficacy of the mixture fenamidone + fosetyl AI on tobacco to control blue mold. Two years experimental trials, carried out following the EPPO PP1/65 (3) methodologies, on "burley" tobacco in southern Italy, demonstrated excellent protectant properties against the agent of tobacco blue mold, Peronospora tabacina Adam. In 2003, in a demonstrative trial, the mixture fenamidone + fosetyl Al applied as the last of three scheduled applications, increased the efficacy and reduced the quantity of mancozeb applied on tobacco plants during the growing season. This fungicide registered for the use on tobacco gives to the growers the possibility to reduce: a) the onset of resistance against the most used active ingredients such as metalaxyl and cymoxanil, b) the quantity of mancozeb applied especially in the region where the harvesting leaf by leaf is the most popular one. In this latter case it is necessary that the days to harvest intervals is the minimum possible. Concluding, this new active ingredient has been registered for the use on tobacco in Italy and is a new possibility to control P. tabacina .