The action of pressure on antigenic materials obtained from culture forms of Trypanosoma cruzi was investigated. The antigens were prepared in a Ribi Refrigerated Cell Fractionator-RF-1 (Ivan Sorvall, Inc.), with temperature control and in an atmosphere of inert gas. The complement-fixation (CF) test, skin test, and the resistance of Rockland strain mice after vaccination were used to study these antigens. The most typical CF curves were obtained with soluble extracts of T. cruzi prepared at less than 10,000 PSI (pounds per square inch). The best skin reactions were obtained with the insoluble portion of an extract of T. cruzi prepared at 20,000 PSI. The antigen used for immunization was not toxic for rabbits, mice, or human beings. The immunizing capacity of this antigen was more effective when it was prepared at less than 10,000 PSI. The survival of mice immunized with this antigen and challenged with a killing dose of T. cruzi varied from 88% to 100% and depended on the number of doses and the quantity of antigen injected. Some of the immunized mice showed transient, low parasitemia after the challenge infection.