Within the framework of the decrees taken on the departments of Isère and Rhone concerning the protection of the population with respect to ambrosia, the object of this study is to relate the analysis of the daily pollen counts in the of air along the Lyon-Grenoble axis. With this intention, three sensors of the type HIRST were positioned according to standards of the European networks in Lyon-Gerland, Bourgoin-Jallieu and Grenoble. The results presented show the curves of the daily pollen counts on the three sites and by indicating the allergic thresholds of risks associated defined by the RNSA. The number of days with high risk, for each of the three sites, can thus be compared. Experiment must be prolonged to follow, these comparative results and moreover, possible effectiveness of the obligations of pulling up of the plant on atmospheric pollination.