Table 1 shows the response of the 24 rice lines with different dwarf genes to GA 3 and bakanae fungus. The elongation was not significantly promoted by GA3 treatment in rice lines carrying either d1 (XHA and XHA-I) or sd6 (CBR34 and CBR34-I) and one of the two lines carrying multi-dwarf genes (B5580A), but was significantly promoted by GA3 in the remaining lines carrying other dwarf genes and multi-dwarf genes. The most sensitive lines were CLA-I and CLA with dc (t) gene, TA with sd1 and sde (t) gene combination,DGWG with sd1 gene, CRH6 and CRH6-I with D53 gene (Table 1). The percentage of increment of seedling length caused by GA3 treatment was much higher for those genotypes than for the other genotypes.