Ginsenosides are triterpenoid saponins of the ginseng plant. Like other saponins, they are fungitoxic (although only slightly) and as such play a role in the interaction between ginseng plants and soil-borne microorganisms. One particularly aggressive pathogen of ginseng is the oomycete Pythium irregulare. This organism is able to metabolize common protopanaxadiol ginsenosides (e.g., Rb1, Rb2, Rc, Rd) via extracellular glycosidase(s) into a common product, ginsenoside F2. This compound may act as either a host recognition factor or a growth stimulant for P. irregulare, allowing it to find susceptible ginseng roots. Our analysis has further demonstrated that the ability of P. irregulare to deglycosylate ginsenosides is directly related to its ability to successfully infect ginseng seedlings. Consequently, our working hypothesis is that P. irregulare uses ginsenosides as a way to both find its host and initiate the infection cycle.