There is growing awareness that the bioactive constituent profile of medicinal plants can be profoundly influenced by endophyte infection. Endophytes are microorganisms (typically fungi or bacteria) that infect plant tissues, often engaged in symbiotic interactions with their hosts. These microbes can produce bioactive compounds themselves, or can alter the metabolite profile produced by the plant. Endophytes can be transmitted to the plant from the environment, or from parent to offspring via the seed. Either way, there is a great deal of variability in the type and extent of endophyte infection observed for a given plant species. This is particularly relevant to the natural products industry, because it can lead to variability in the bioactivity of plant medicines, even when they are prepared from the same genus and species of a given plant. Our research group is currently engaged in collaborative research projects with Dr. Stanley Faeth at the University of North Carolina Greensboro Department of Biology and Dr. Nicholas Oberlies at the University of North Carolina Greensboro Department of Chemistry that seek to elucidate the role of endophyte infection in the bioactivity of several medicinal plants.