Initially the authors review the bibliography concerning problems of transmission of Chagas' disease through blood transfusion. Emphasis is given to the various aspects to call attention to the possible occurence of this fact. The confirmation of this possibility in man, the high incidence of chagasic infection in blood donors found in various blood banks and the prophylactic methods that should be adopted are discussed. At the blood bank of the Hospital das Clinicas in Goiânia, the prevalenee of chagasic infection has been observed in blood donors and evaluated through the Guerreiro and Machado test at 10,43%. With the finality to verify the sensibility of the Guerreiro and Machado reaction in the selection of blood donors, the examination was repeated in 452 donors, once or more, in different times, zohen the various blood donors would come again to donate blood. Concording results were observed in the reaction of 427 (94,47%) and discording results in 25 (5,53%). The authors emphasize the risk involved in the selection of blood donors using the Guerreiro and Machado test as a safeguard even when it has been repeated more than once. Finaly, the authors consider that at the present time the ideal method to prevent the transmission of Chagas' disease through blood transfusion is the addition of gentian violet to any blood to be transfused, in endemic areas as in other areas, whenever the donor might have epidemiologic antecedent.