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azadirachtol (9) were isolated from seed kernels of Azadirachta excelsa. Their structures were established by spectroscopic techniques, and the structure of 3 was confirmed by X-ray analysis. Compounds 1-7 and 9 exhibited toxicity to the diamondback moth (Plutella xylostella) with an LD50 of 0.75-1.92 íg/g body weight, in 92 h. The genus Azadirachta (Meliaceae), which occurs in the tropics, contains only three species, Azadirachta indica A. Juss, A. siamensis Valeton, and A. excelsa (Jack) Jacobs. Thailand seems to be the only country in which all three species exist. The Indian neem tree (A. indica) grows mainly in the coastal area, and Thai neem (A. siamensis) grows widely in all parts of Thailand.1 A. excelsa is found in the southern part of Thailand, and its local name is “Tiam ” or “Sadao chang”.1 The Indian neem tree has been investigated intensively worldwide during the last three decades. More than 200 compounds have been isolated fro