Electron microscopic observation of Trypanosoma cruzi epimastigotes reveals the presence of microbody-like structures (microperoxisomes) in which 3,3'-diaminobenzidine (DAB) is peroxidized to electron-opaque material. The role of peroxidase in DAB peroxidation is supported by the enzyme demonstration in disrupted epimastigotes and the microbody-containing cell fractions.