Mosquitoes and bed bugs may play a role in the transmission of hepatitis B virus (H.B.V.). We investigated this possibility with the Triatoma Infestans, which is a hematophagous insect widely prevalent in the Argentine Republic. Triatoma Infestans fed with serum or blood contaminated with H.B.V. were studied at 7, 14, and 21 days after contamination. Stool and insect homogenates were positive for HBsAg at each time checked. Considering the domestic habits and hematophagous condition of Triatoma Infestans, we feel that this insect could also play a role in the transmission of H.B.V. through their bites or dejections.