Feeding behavior and some antihemostatic properties of the saliva of Rhodnius prolixus infected with Trypanosoma rangeli were studied and compared with those of uninfected controls. Insects with salivary gland infection pierced host skin more often and drew less blood and at a lower rate than controls when feeding on a rabbit. None of these differences was observed when feeding was performed through a membrane feeder. Salivary gland homogenates from infected insects, at 30 days after feeding/infection, had a significantly lower amount of total protein/salivary gland pair and less anticoagulant activity than controls. Also, infected salivary glands exhibited significantly reduced apyrase activities and reactive nitrogen groups when compared to controls. It is concluded that salivary infection of T. rangeli impairs the ability of the vector to locate blood vessels by affecting salivary antihemostatic properties, thus enhancing the possibility of intradermal inoculation of parasites into the mammalian host.