Trypanosoma cruzi chromatin is not condensed in chromosomes during mitosis. In previous studies a characteristic H 1 was not found in SDS or in acid-urea-PAGE. Consequently, it was proposed that the particular behavior of T. cruzi chromatin in dividing cells was due to the absence of an H 1 histone. In the present work, histones from this parasite were systematically characterized by spectrofluorometric analysis, amino acid composition, PAGE in one and in two dimensions, differential extraction with PCA and TCA, immunological cross-reactivity with antisera, and immunoblotting. We conclude that T. cruzi contains all five histones, H 1 presenting solubility and immunological properties similar to those in other species, but with a particular electrophoretic mobility in Triton-PAGE. Thus an explanation other than the absence of H 1 should be offered in order to understand the behavior of T. cruzi chromatin during mitosis. Moreover, histone variants were described by two-dimensional PAGE. The presence of histone variants suggests that they may participate in the regulation of cell proliferation and differentiation of this parasite, as it has been postulated for higher eukaryotes.