Blood-feeding Triatoma infestans obtained its fills from immune chickens in 15 min, but it needed 40 min for feeding upon non-immune chickens. High-titer specific IgGs and skin reactivity against T. infestans saliva antigens were elicited in immune chickens. Fluorescence-labeled leukocytes from non-immune or immune chickens were used to determine sources of blood drawn by equal numbers of triatomines distributed in separate compartments of a hut-like box. It was shown that 64.4 ± 4.7% of the reduviids were captured in the immune chicken room; 35.6 ± 4.5% were present in the non-immune chicken dwelling, and these differences were statistically significant (P < 0.001). Furthermore, T. infestans feeding upon immune birds reached the adult stage 40 days before those feeding upon non-immune birds, and differences were statistically significant. These results appear to have a broad epidemiologic significance as for spreading enzootics; hence, the immunologic status of vertebrate host populations appears to favor T. infestans as the main transmitter of Trypanosoma cruzi.