Summary 1. Trypanosoma duttoni survived in experimentally infected Triatoma gerstaeckeri for about two to three days. During this period no multiplication occurred. The flagellates gradually became sluggish, motionless, and disintegrated; at the end of 72 hours no viable trypanosomes were found. Similar tests, performed on other rodent trypanosomes, yielded similar results. 2. Triatoma, which had been experimentally infected with Tr. duttoni and which in three days and later were crushed and inoculated into normal mice (Mus musculus), invariably failed to produce infection.