The plasmas of normal subjets and of patients with chronic Chagas' disease were intentionally contaminated with a very virulent strain of Trypanosoma cruzi. The specimens were frozen to -20°C during three and twenty-four hours and for three, seven, fourteen and twenty-one days. After the aliquots were warmed to ambient temperature, they were examined as a fresh smearunder contrast phase microscopy, cultivated in Warren’s medium and inoculated in mice for subsequent histopathological examination of the heart. The results indicated that freezing durlng three and twenty-four hours did not prevent survival of the infecting parasite. The purpose of the study was to contribute to the orientation of plasma transfusion in blood transfusion centers. Since plasma transfusion is commonplace in, this country, many times colleeted from infected donors with Chagas disease, we wish to decry the notion that low temperatures securely promote sterilization.