Karyological examination of 26 species of bats from the family Phyllostomidae revealed two Y chromosomes (XY1Y2) in six species involving three genera. All females are of the XX constitution. Meiotic studies demonstrate the origin of the additional Y in Carollia to be the homolog of an autosome translocated to the X element. The origin of an additional Y in Artibeus is best explained as a separate event. In one species of Artibeus (A. turpis) a centric fusion of the two Y elements is emphatically suggested.