The chromosomes of the nine-banded armadillo, Dasypus novemcinctus, were studied using cultured peripheral leukocytes, tissue cells and direct preparation of male germ cells. The diploid number was found to be 64 in the blood and tissue cells, the haploid number was 32 in the testicular preparations. The autosomes can be divided into six groups, according to their size and the position of the centromere. Group A contains two pairs of large metacentrics, Groups B and C contain together 18 pairs of acrocentric chromosomes, the distinguishing feature being a gradual decrease in size. Group D is composed of six pairs of small metacentric chromosomes with almost medial centromeres. One prominentld satellited chromosome constitutes a ready marker element of this groud and of the karyotype. It is not entirely certain whether this satellitey chromosome has a homologue or not. Five pairs of small acrocentrics constitute Group E. These are almost indistinguishable from one another. Buccal smears showed a typical sex chromatin body in interphase nuclei of epithelial cells from female animals similar to that observed in some other mammals. A sex difference was also noted on examination of peripheral blood films, typical “drumsticks” being present on polymorphonuclear leukocytes from female armadillos.