Five horticultural forms of Carica papaya growing in India have been studied. Karyotypes of them represent homogeneity. Slight structural difference in chromosomes of different varieties is noticed, which proves the role of structural alteration of chromosomes on the evolution of the forms. No heteromorphic pair, or unpaired chromosome or any chromatin body, suggesting chromosomal basis of sex difference in the species, could be recognized. © 1971, Japan Mendel Society, International Society of Cytology. All rights reserved.