Pea powdery mildew caused by the obligate biotrophic fungus Erysiphe pisi is an air-borne disease of worldwide distribution. Powdery mildew affects all green parts of pea plants. The first symptoms are small, diffuse spots on leaflets and stipules, usually first appearing on the lowest part of the plant. Its infection can be reduced in pea (Pisum sativum) by exogenous applications of chemicals, such as BTH and BABA. This protection is known to be related with the induction of the phenolic pathway but the particular metabolites involved have not been determined yet. BTH and BABA treatments changes in phyto-alexin content and development of the resistance to pea rust. These chemical treatments were effective against E. pisi. The enzyme activity PAL, PPO and CAT increased in leaves during infection by E. pisi and protected the plants from disease by SAR, detoxification of ROS by stabilizing sub cellular structures. Detailed analysis through highperformance liquid chromatography (HPLC) showed qualitative and quantitative differences in the content, as well as in the distribution of phytoalexins