Cell infection with Trypanosoma cruzi, the agent of Chagas' disease, begins with the uptake of infective trypomastigotes within phagosomes and their release into the cytosol, where they transform into replicating amastigotes; the latter, in turn, differentiate into cytolytically released and infective trypomastigotes. We ask here if the T. cruzi infection program can develop in enucleated host cells. Monolayers of L929 cells, enucleated by centrifugation in the presence of cytochalasin B and kept at 34 degrees C to extend the survival of cytoplasts, were infected with parasites of the CL strain. Percent infection, morphology, stage-specific markers, and numbers of parasites per cell were evaluated in nucleated and enucleated cells, both of which were present in the same preparations. Parasite uptake, differentiation and multiplication of amastigotes, development of epimastigote- and trypomastigote-like forms, and initial cytolytic release of parasites were all documented for cytoplasts and nucleated cells. Although the doubling times were similar, parasite loads at 48 and 72 h were significantly lower in the cytoplasts than in nucleated cells. Similar results were obtained with the highly virulent strain Y as well as with strains CL-14 and G, which exhibit low virulence for mice. Cytoplasts could also be infected with the CL strain 24 or 48 h after enucleation. Thus, infection of cells by T. cruzi can take place in enucleated host cells, i.e., in the absence of modulation of chromosomal and nucleolar gene transcription and of RNA modification and processing in the nucleus.