A method is described for the isolation and purification of trypomastigotes and amastigotes of Trypanosoma cruzi from cell cultures. L-A9, a transformed fibroblast cell line, and J774G8, a macrophage-like cell line of tumor origin, were used. Both cell lines were infected with bloodstream trypomastigotes of T. cruzi, which once within host cells transform into dividing amastigotes. After 6--8 days infection the host cells ruptured, spontaneously liberating parasites into the culture medium. L-A9 cells liberated mainly trypomastigotes while J774G8 cells liberated amastigotes. The parasites were collected and purified by centrifugation in a gradient of metrizamide. The purity of the preparation as well as the morphology of the parasites and the host cells were analysed by electron microscopy.