Jusqu'en 1990, au Maroc, les attaques de mildiou sur tournesol étaient restées discrètes; en 1991, un foyer est repéré; en 1992 la maladie prend des proportions inquiétantes. Cet article présente les travaux entrepris par la recherche agronomique marocaine, en collaboration étroite avec l'INRA en France, pour y faire face. Owing to the risk of downy mildew extension on sunflower in Morocco, the article shows the various actions led by Morocco-INRA, in connection with other moroccan Ministry services, and in collaboration with France-INRA : surveys to determine the importance of the disease, race identification, a discussion about chemical treatment and a test on its efficiency in the local conditions, as well as trials belonging to genetic improvement. These trials have resulted in the creation of the first two Moroccan hybrids and should lead quickly to two resistant populations-varieties, deriving from the best adapted Moroccan varieties to the dry conditions.