Abstract
Genetic studies on resistance to brown planthopper in some rice varieties, in which reslstance genes had been found but not identifled, were conducted. Allelism tests revealed that resistance of 'Col. 5 Thailand', 'Col. 11 Thailand' and 'Chin saba' was governed by a recessive gene that was designated bph 8(t), and that resistance of 'Balamawee', 'Kaharamana' and 'Pokkali' was governed by a dominant gene that was designated Bph 9(t).