Two samples of Narthecium asiaticum Maxim leaves collected in Japan were found to contain 103 µg g−1 and 160 µg g−1 dry matter of 3-methoxy-2(5H)-furanone respectively. 3-Methoxy-2(5H)-furanone was suggested to be the toxic principle of N. asiaticum causing nephrotoxicity in cattle in Japan. Two other furanones, which are thought to be non-toxic, were also isolated from the two samples. These were 4-methoxy-2(5H)-furanone and 5-hydroxy-4-methoxy-2(5H)-furanone. Copyright © 1999 John Wiley & Sons, Ltd.