Under laboratory conditions as well as in nature concentrated malathion ULV was found to have a lethal effect on eggs of the following species of triatomine bugs: P. megistus, T. infestans, T. brasiliensis, T. sórdida, T. phyllosoma, R. prolixus e R. neglectus. This lethal effect of Malathion was more intense on newly laid eggs. Even though mud inactivated the ovicidal effect strongly the field observations seem to demonstrate that Malathion spraying offers possibilities for the control of the vectors of Chagas' disease mainly through the extermination of the eggs of the hemiptera.