The elongation response of 17 near-isogenic dwarf lines of the Shiokari rice cultivar to gibberellins (GAs) was examined. Two strains, ID-18h and ID-19, were selected for further analysis of their endogenous GA levels. It is suggested that ID-18h dwarfism is caused by the deficiency of GA 3 beta-hydroxylation activity, and ID-19 dwarfism by the insensitivity of the elongation response to physiologically active GAs.