Dsec\I-element and Dmau\I-element are more closely related to the chromosomal I-elements of D.melanogaster than to those in any species. No sequence difference is observed between 2 chromosomal I-elements from D.melanogaster and one from D.simulans. This supports the idea that defective chromocentral I-elements of D.melanogaster originated before the species diverged and the chromosomal I-elements were eliminated. Chromosomal I-elements recently reinvaded natural populations of D.melanogaster, possibly by horizontal transfer from D.simulans.