It has been recognized empirically that the application of a rice blast controlling agent IBP(0, 0-diisopropyl-S-benzylthiophosphate) in an appropriate dosage gives the shortening effect on rice plant culm and this side effect is of use to keep the plants from the prostrating damage by wind at their harvesting time. The length of culm in a rice plant with or without application of IBP has been related by five partial regression coefficients to the length of internodes. The analysis of variance of multiple regression equations shows that 94 and 88% of variation in the length of culm could be attributed to variation in the length of internodes with and without application of IBP respectively. Every contribution of length of five internodes to the length of culm was significant but they did not contribute equally to the length of culm. The magni tude of shortening in each internodes varies widely depending upon the time of application of IBP. The shortening effect of IBP on rice plant have been proved by comparing these two multiple regression equations. Although the bi's for plots with and without IBP application were of the same sign and similar in magnitude, the slopes differed significantly. The test for a difference in position between the two equations for plots with and without application of IBP gave a nonsignificant F.