Different tissues and organs of mice infected with Trypanosoma cruzi trypomastigotes have been examined for the presence of parasites and parasitic antigens during both the acute and the chronic phases of infection. Specimens of skeletal and cardiac muscles, spleen, liver, brain and sciatic nerves were studied by histological and immunological methods. During the acute phase of infection, the parasites were commonly observed in these tissues. In the chronic phase of the experimental infection, pseudocysts filled with amastigotes were seen in less than 1% of the tissue sections, while immunohistological methods showed that T. cruzi antigens were present in 11% of the inflammatory infiltrates. These findings suggest that antigenic stimulation persists throughout the chronic phase, even though the parasites are not morphologically detectable.