A method was devised for the extraction of phytoalexins from leaves challenged with pathogens. The leaves are harvested from intact plants and phytoalexins are extracted by vacuum infiltration with aqueous 40% ethanol and shaking them in the ethanol solution for several hours. Phytoalexins were readily isolated from the filtered solutions. The method gave relatively efficient recovery of phytoalexins from soybean [Glycine max] plants inoculated with Pseudomonas glycinea [P. syringae] and flax [Linum usitatissimum] plants inoculated with Melampsora lini with minimal quantities of interfering compounds. By using the new technique putative phytoalexins also were recovered from the leaves of pathogen-inoculated celery, sunflower and wheat plants.