The effect of thuricide, a commercial preparation ofBacillus thuringiensis Berliner var.Kurstaki was studied on different stages of rice stem borersScirpophaga incertulas, Sesamia inferens andChilo auricilius. It was found to be ineffective on the eggs,pupae and adults of these borers. All the agegroups of the larval stages got infected. Thuricide was almost equally effectiveat 1·0, 0·75, O·50and 0·25%concentrations. 1% concentration, sprayed at the time of hatching of the larvae, reduced the incidence of dead hearts by 76·36%, white heads by 67·45% and the number of living larvae inside the tillers by 76·87%. It persisted for 15 days or more under green house conditions.