The karyotypes of Mycteria americana (Ciconiidae) and Platalea ajaja (Threskiornithidae) are described. Both species have a diploid number of 2n = 72. There are slight chromosome morphology differences, which could be related to distinct chromosome evolution pathways of these two families. Besides a better understanding of the chromosome relationships among Ciconiiformes, this first chromosome characterization of M. americana and P. ajaja is an important tool for the conservation of both species.
