We previously identified by immunoscreening Trypanosoma cruzi cDNA libraries a group of proteins containing long stretches of tandem repeats. The goal of the current project was to gain insight into the functions of these proteins through ultrastructural analyses consisting of western blotting and electron microscopic localization studies. By comparing western blots of total parasite lysate and different fractions of T. cruzi, we found that 3 of the repetitive antigens are exclusively associated with the parasite membrane, or cytoskeleton, or both. One of the 4 repetitive antigens studied has some association with the membrane or cytoskeleton but also appears to be free in the cytosol. In immunoelectron microscopic studies, the 4 repetitive antigens were detected in different intracellular locations. One of the proteins is located between the flagellum and parasite body, the second has a nuclear distribution, the third is associated with the cell membrane, and the fourth is dispersed throughout the cytoskeletal network. These findings suggest that despite the general structure similarities of these repetitive proteins, they may serve different cellular functions.