It was decided that the Izu Experimental Station for Medicinal Plants, National Institute of Health Sciences in Japan would close in March 2003. This experimental station has over 60 years history and a collection of more than 500 medicinal plants from all over the world. The allelopathic activity of most of these medicinal plants has never been studied. Therefore we evaluated the allelopathic activity of 239 medicinal plants using the newly developed sandwich method as a standard bioassay to make use of these valuable resources.